Free Biology NEET Video Lectures for Plant Growth And Development

00:00:01 [Music] welcome students today we are going to study plant growth and development so how do plants have different structure and functional attributes you know that the plants have seeds roots stems leaves flowers and fruits all this form a part of the plant growth cycle in turn involving plant growth and development now the question arises why do we need to study about plant growth and development as we all know we use plants in our day-to-day life for various applications including food medicine paper

00:01:28 for textiles we use plants for wood used in constructions and we use it as a feeding livestock now in order to accomplish all these applications a sound knowledge of plant growth and development is essential for assisting its healthy cultivation that's the reason why we must know about the plant growth and development so in this chapter we are going to study about in general the plant growth what is the process of differentiation d differentiation and redifferentiation in plants then in plant development we will study

00:02:16 about the role of plant growth regulators photoperiodism vernalization and then how to overcome seed dormancy so now what is plant growth now growth is a characteristic of a living organism isn't it so in order to define it is an irreversible or permanent increase of a size of organ or its part or the individual cell now for this it would require energy in the form of atp and it is accompanied by metabolic activity which is a club of all anabolic and catabolic reactions now let's see which of the following can be considered

00:03:15 as plant growth can you people make out yes the picture of the leaves and the plant shown on the right hand side of the slide shows expansion of the living matter which is leaf while on the left hand side it is swelling of wood piece when placed in water so can you make out which will depict plants growth yes the expansion of leaf will be considered as the result of plant growth as there is an increase in organ size due to metabolic activity which takes place with the help of atp consumption while in the swelling of the wood placed

00:04:11 in the water it happens due to the endosmosis of water so there is no metabolic reaction which is causing the swelling of wood now how do plants grow in nature this growth in various different regions of the plant happens due to a set of cells which form a region called as meristem and these places are called as meristematic regions of the plant where there is rapid cell multiplication happening so plants they retain their capacity for unlimited growth throughout their life that is a very interesting and a peculiar property

00:05:00 which the plants have that they can retain their property of unlimited growth till they are alive this happens due to the presence of these meristems or meristematic regions in the plant the cells in these regions they are capable of continuous cell division and self perpetuate so as you can see on the picture as you can see on the slide the photograph shown is for the meristematic cells so mary stem cells they continue to divide to form new cells and these new cells then some of the cells they

00:05:48 differentiate to form parts of the body's plant body so this is called as open form of growth let's see what are the different types of meristems so if we can see on the slide here there are black boxes encircling regions on the plant these depict different types of meristematic regions present in the plant at the top here of the plant you see a region which is called as apical meristem there is a microscopic picture of the section here where you can see the shoot apical meristem shown by the green arrow here this

00:06:43 region it is found in the terminal bud of the plant lengthening of the the increase in the top region length of the plant the bottom most region the black box shown here this depicts the roux typical meristematic region a route apical meristem which is responsible for the elongation of the root to go deeper into the soil the third type of meristem is called as lateral meristem shown in between here with a rectangular box now lateral meristem is the region which is responsible for enhancing the width of the plant

00:07:47 which means the the cork or the vascular cambium region the increase in those regions if you remember the vascular cambium it includes xiamel xylem and phloem elements and the cambium is responsible for the growth in the bark region of the plant so these form the lateral meristems and also the axillary meristem which is responsible for branching to happen showed here in the nodal region so this is another kind of meristem which is responsible for the formation of new branches let's talk about what are the different

00:08:42 phases of growth which can be observed in plants now just to give you an example we will take root as the model system and here we have demonstrated the various phases of growth in a root system so you can see at the tip is the region which is called as root cap and as we go up the root we see the regions of elongation with root heads which is a more matured region so let's talk about the bottom most region which is marked here as root cap this is the region which has meristematic cells now these meristematic cells they are

00:09:34 rich in protoplasm they possess large and clearly visible nuclei the cell walls are thin and rich in cytoplasmic content so they are abundant plasmodesmeta connections also which you can find above the meristematic regions is the elongation region where the cells they'll have increased vacuolation the cells will be more enlarged and the new cells will get and there is new cell wall deposition so the cell wall becomes thicker the yellow color region shown here with the root hairs is called as the maturation

00:10:34 part of the growth in which the cells will attain maximum size there is no more division happening the cell wall has thickened and the there are protoplasmic modifications where you can see extensions in the form of root hairs so this is how growth happens in a root system now the question arises how do we measure plant growth at a cellular level you can see there is nucleus cytoplasm which combined is called as protoplasm so when there is growth happening there is increase in the amount of protoplasm

00:11:33 now there are different parameters which are used to measure plant growth now i hope you can understand that it is not possible practically to measure growth at the intracellular level all the time so there are indirect parameters which have been brought in to depict the plant growth like for example plant growth can be depicted in terms of fresh weight or dry weight mass or in terms of cell numbers increase the rate at which the cell number is increasing and if it is one dimensional then we can

00:12:18 measure the length of the plant two dimensional area wise and three dimensional volume wise now mathematically there are two ways by which we can calculate the growth rate in plants one is called as arithmetic growth now the increased growth per unit time this will be growth rate so anything rate means we are determining per unit time so growth rate would be the rate at which the growth is happening plant or plants organ they can produce more cells through arithmetic growth or geometric growth patterns or in fact you can also

00:13:08 observe them happening simultaneously now let's understand what is arithmetic growth and under what conditions you can assume that it is arithmetic growth now in mitotic cell division in plants now one of the cells which has divided which will again continue to mature and differentiate while the other cell will continue to divide using mitotic division so if you can see on the slide the two blue cells here it will lead to daughter cell one of the daughter cells is continuing to divide while the other daughter cell

00:13:59 will then keep maturing so this maturity happens because of its differentiation and gets added up to plant tissue or plant organ as per requirement so you can see like for example in root elongation there is a picture which shows the root growth in 10 20 30 40 and 50 days interval so if we want to depict the rate of growth in this root we can use the expression for arithmetic growth happening at a constant rate where the length of the root at any given time t can then be given as the initial length of the root

00:14:57 plus the rate at which the root is growing and the time total time in which you want to determine the length so we can say that dl by dt because the rate at which the length of the root is changing we are assuming it is constant which here it is being depicted by r so if you will integrate using the limits let's assume at time t is equals to 0 it was at some initial value l naught and at time t it is at some value l with a subscript t so if you will integrate your rhs of the equation becomes l

00:16:00 and it becomes r d and we have the limits 0 to t and here the limit is l naught to l t so if you put the limits it will become l t minus l naught is equal to r times t minus 0 so which is same as given here now this is a linear equation so if you will make a plot as shown here in the yellow color of length of the elongated root which is lt versus time then it will be an inclined straight line with a y intercept of l naught i hope this is understood and the slope of this line is nothing but your

00:16:59 r which is the rate of growth of the root which is here assumed to be constant as you can see from the incline straight line the slope is same now let's see how we determine geometric growth in plants geometric cell division it results if all the cells of the organism or the tissue are active and are continuously dividing via mitotic division so in that case what will happen the two cells will lead to four cells the four cells will lead to every cell leading to two so they will again lead to eight cells

00:17:59 then these eight will become 16 and so on so this is a geometrical growth pattern now in geometrical growth pattern one can see different phases of growth if you will make a plot in terms of size or weight of the organ versus time one can see three distinct phases of growth which we call as the first phase lag phase where there is no significant change in the size or weight of the organ or the plant then comes the active growth phase which is called as exponential phase and then after the nutrient depletion

00:18:52 happens there is reduction in the growth rate and eventually there is no more growth happening so it follows more or less a sigmoidal growth pattern now in the active growth phase which is depicted here as an exponential phase if we have to determine the growth rate of this plant or the organ or tissue then we can use an exponential equation to find the growth rate so in that case let's assume the y axis is in terms of weight of the organ depicted here as w 1 and w naught is the initial weight

00:19:51 so then with respect to time this is the exponential function the rate at which the weight of the plant is changing is proportional to the weight of the plant so mathematically when this proportionality constant goes out there is a constant which comes in which has been given a notation small r and we have w so if you want to make an equation with respect to w we will integrate this as we did earlier let's see put the limits here given as w naught initial value and sum at some time t they have given it as 1.

00:20:40 so let us put as 1 or t so time here initial is 0 and at some time t when the w is w1 so if you will integrate this you will get ln w and putting the limits w1 by w naught is equals to rt t minus 0 so we can say as rt so then writing it in terms of exponential function the ln will go as it is a base to the base of the natural logarithms so your w1 by w naught will become equal to e to the power of rt and w1 therefore becomes w naught multiplied by e to the power of r t as shown here so this is how

00:21:49 we reach to the exponential growth expression for geometrical growth pattern in plants you can even see this pattern in the seasonal variation observed in trees when the leaves are falling then there are fresh leaves coming and when the leaf buds are dormant during the winter season so you can also depict that change in terms of geometrical growth pattern now we have come to know what is arithmetic growth and what is geometric growth here we have stated an example where one can see both arithmetic and geometrical growth

00:22:47 pattern during plant growth and development so here the picture shows embryo of the bean seed and during the embryo development phases when it's begin with the zygote the zygote divides using geometrical growth pattern keeps dividing it then slowly matures to a phase where not all cells keep dividing but some of the cells they keep dividing they retain division while the other cells they tend to lose capacity to divide and they start maturing and differentiating to function various other roles

00:23:34 in the embryo development until it becomes a seedling let's talk about absolute and relative growth rate now what is absolute growth rate it is the increase in the total growth of the plant per unit time while relative growth would be growth of the given system per unit time per unit the initial value of the parameter like for example to understand it better let's take this problem there are two leaves as shown here leaf one and leaf two leaf one being smaller initial size is five centimeter square

00:24:25 after ten days this small leaf reaches a size of ten centimeter square shown here in the form of dotted picture similarly leaf 2 also in 10 days initial size which is much bigger which is 50 centimeter square in 10 days it increases to a size of 55 centimeters squares now let's see how we can differentiate between the growth of the two leaves if you see the absolute growth rate in the two leaves it amounts to the same value so what is absolute growth rate as i mentioned earlier this is the increase

00:25:21 in the area in this case per unit time so the increase in area the difference is the same in both the cases leaf 1 and leaf 2 which is 5 and this happened in 10 days so your absolute growth rate would be 0.5 centimeter squares per day isn't it as shown here now if we want to compare the growth in the two leaves because the initial size is different absolute growth rate may not be the right way to make comparisons hence in order to normalize the difference in the initial values we make use of another parameter which i

00:26:15 just mentioned which is called as relative growth rate which will take into account the variation in the initial values of the parameter so here we were depicting the change in the area to monitor the growth so now initial area being different in both the cases if we use that also in the expression we should be able to negate the effect or the difference in the initial values of the area so then the relative growth rate in this case can be written as the change in the area per unit initial area

00:27:05 happening in the given amount of time so in both the cases the difference in the final and the initial area is point is 5 while in one case the initial area is five and in the other case the initial area is fifty so five by five divided by ten days and in the second case it will be 5 by 50 divided by 10 which is the time so here it becomes 0.1 and here it becomes 0.01 so now you can see that in terms of relative growth rate leaf 1 has a higher relative growth rate than the leaf two so this can be used for making

00:28:10 comparisons talking about the conditions for plant growth what makes the leaves to increase in size what facilitates this process of cell enlargement or the metabolic activity now after reading the chapter on plant nutrition we know that what are the basic requirements which lead to plant growth and development now water we know it will help in cell enlargement it is also utilized in metabolic reactions important for enzyme activities oxygen is a gaseous nutrient which helps in releasing metabolic energy light

00:29:01 again it helps in generation of energy then neutrines anyways these are required for synthesis of cellular content gravity gravity is another parameters which is important one of the parameters which is important for lengthening determines the length of the plant and the length of the roots then optimum temperature which is also very crucial for the growth of the plant because it can impact the metabolism of the plant in terms of enzyme activities and the reaction rates now what happens during plant growth in the cells

00:29:49 plants the change in the growth of the or the development of the plant is governed by three phenomenas happening at the cellular level which is differentiation then d differentiation and again redifferentiation now let us talk about these three processes differentiation it is a process of maturation of cells which are derived from meristems to perform a specific function so meristems we know those are the regions where the cells continue to divide so they are actively dividing cells now these cells they then undergo

00:30:37 structural changes in the cell wall and their protoplasm like here in case of root or in the stems you will find that some of these cells will mature to become the xylem elements here we have shown the vessel elements and the trichards which are different type of xylem elements required for the transport of water so d differentiation what is it it is the process by which differentiated cells again regain the capacity or the ability to divide so they return back to the ability to divide so when i was talking

00:31:28 about differentiation i said that the actively dividing cells they stop dividing they lose the capacity to divide and in the process mature to perform a specific function now in case of d differentiation a matured cell which is performing a specific function will revert back to a stage of meristematic activity which means it will start to continuously divide like for example the parenchyma cells i am sure you must have heard about this term and you must have learnt about it now these parenchyma cells their major

00:32:09 role in the plant is like storage or to become the flesh of the plant then the packing material now these parenchyma cells for example they also d differentiate revert back to meristematic state where to help in the intra fascicular cambium or in the core cambium and they facilitate in the secondary growth of the plant in this case it will increase the grid of the stem so this is a picture where you can see a cross section of the stem where the parenchyma cells they have been modified to play a role in the

00:32:57 inter fascicular cambium and the core cambium thereby increasing the layers of the cells in the core clear and also in the cambium region the vascular cambium region here so vascular bundle is also shown here the xylem elements shown in the pink now talking about the third term which was re-differentiation process by which a d-differentiated cells gain the ability to divide and perform the specific function now once a cell has the differentiated again it is re-differentiated to perform a new set of function

00:33:50 so that is redifferentiate so vascular cambium which is a d differentiated cells from the parenchyma cells and they again get re-differentiated to form the secondary xylem or the phloem so this process can the example which i quoted last in the last slide is a good example to show the conversion of or the process of differentiation d differentiation and redifferentiation similarly cambium which is again a d differentiated cells they will undergo the process of redifferentiation to form the cork

00:34:41 which is the protective or the waterproofing in the plant so this is how secondary growth enhancement will happen in a plant you can see the picture here the core clear the which increases because of the core cambium and the secondary phloem and the secondary xylem which enhances or increases due to the vesicular cambium present and they form the wood of the plant talking about development process it includes growth and differentiation it is a term that includes all the changes that an organism goes through

00:35:30 during its life cycle from germination of the seed to its senescence as you can see from the picture shown for sunflower plant starting from the seed then a seedling a small plant lead growing to a mature plant flowering of the plant and then leading to senescence plasticity is defined as the ability of the plants to follow different pathways in response to the environment or phases of life to form different kinds of structures a very good example which you can see in nature is the heterophili in coriander

00:36:15 leaves at the germination stage you can see the leave structure is different while at maturity the leaf structure is completely different it gets broadened another example in nature is the heterophily in buttercup leaves where the leaves which are under the water they are have a thinner morphology while which are exposed to the aerial region aerial part where they are exposed well to the sunlight the leave structure changes and they become broad and biden now let's see what are the factors that

00:37:02 control plant development there are in intrinsic factors like the genetic makeup of the plant and the presence of certain components here abscisic acid is one of the plant growth regulators another is extrinsic factors which includes light temperature water oxygen nutrition so today we will discuss more about plant growth regulators now plant growth regulators these are chemical messengers which are defined as organic substances which are synthesized in very less quantities in a part of the body

00:37:58 and they can be transported to another part of the body as per the requirement where they would influence a specific physiological process so there are various different kinds of plant growth regulators we will study about the three classes one auxins another gibberellins and cytokinins are plant growth promoting hormones or regulators talking about the regulators which are growth inhibitory these are ethylene and abscisic acid you must be wondering why is the plant at all producing something which is inhibitory to its

00:38:53 growth but you will see later as we move on that how crucial it is for the plant to regulate its growth as well and how does it help the plant so talking about auxins now in little more detail so there is a picture of a plant which has coleoptile regions the tip of these plant leaves gras it is canary grass which is shown here now they are found to elongate the cells of the tip region which is collectiles upon illumination so when the light falls on it one can see these cells elongating this happens

00:39:44 due to the presence of a natural auxin which is called as indole 3 acetic acid and indole butyric acid so these are natural auxins which are present which are said to be responsible for this elongation process this can also happen using synthetic auxins man-made auxins for example nepthalinic acid acetic acid nephthylene acetic acid and 2 4 d so 240 is a short form of 2 4 dichlorophenoxy acetic acid now these natural auxins they are produced by the growing episodes of the stems and the root this

00:40:32 can prevent fruit and leaf drop at an early stage auxins they are also used to initiate rooting in the stem cuttings you can see the picture on the slide here where when the stem cuttings they are insert in a solution nutrient medium where auxins are provided the routing starts happening they promote root formations they are also used for or to induce parthenocarpi you must have heard about seedless orange and fruits so they induce epical dominance thereby reducing lateral growth but the apical growth will happen

00:41:35 so they will will dominate they are also used in agriculture in the form of herbicides let's talk about another class of plant growth promoting hormones which is gibberellins now giprylic acid this was first discovered in the fungal pathogen called as gibrala fusicori they caused the disease called foolish disease of rice seedlings later the same compound was detected in the plants now giprylic acid it is used to increase the in agriculture to increase the length of the grape stalks you can see the picture

00:42:29 on the slide in the absence of the gibralic acid and when gibralic acid is sprayed then the white difference which you can see in the length of the grape stalks so it hastens the maturity period like for example from flowering to fruiting so which is beneficial in agriculture and it also delays senescence so can you guess what benefit can be achieved from this property in agriculture industry or in your fruits right i hope you have guessed it so you can extend the market period of the fruits it also promotes bolting

00:43:24 here an example in rossiter leaves you can see the significant difference between the untreated plant and the treated plant where lengthening of the internodal region just before flowering can be promoted let's talk about the third plant growth promoting hormones or regulators which are called as cytokinins cytokinins they are known to induce rapid cell division in plants it was first discovered in the autoclaved sperm dna from herring herring is the fish and the kinetin was the first cytokinin which was discovered in

00:44:22 its sperm dna later it was found to be produced in plants zeatin is another cytokinin which is identified in corn kernels and coconut milk they are generally found near the root episodes shoot buds and in the young fruits you will find higher concentrations of cytokinins at these places in the plant contrary to auxins cytokinins they promote lateral growth so they'll promote the growth of lateral buds and therefore they will suppress the epical bud dominance and they also delay senescence by

00:45:22 promoting nutrient mobilization one of the other plant growth regulators is ethylene ethylene is used by the plants to promote senescence and abscession of plant organs specially of the leaves and the flowers it breaks the seed and the bud dormancy it also promotes root growth ethylene is also highly effective in fruit ripening as it enhances the respiration rate during ripening of the fruits in deep water rice plant one can see ethylene promoting rapid internode and ptole elongation ethylene can be made

00:46:30 available to the plants exogenously through the precursors which is available commercially it is ethophone growth inhibitors or regulators is abscissic acid it was discovered to cause abscession of cotton buds or cotton balls it inhibits seed germination which can be a protective mechanism by the plant during adverse conditions so it will prevent sprouting during unfavorable conditions like desiccation it helps to by stimulating the closure of stomata in case of drought conditions so thereby reducing the evaporation of

00:47:20 water so it acts like plant growth inhibitor which can be a response to any environmental stresses like cold temperature or dehydration so now i'm pretty sure you must have made made out that gibberellins abscisic acid these are antagonistic now let's talk about a phenomena called photoperiodism in plants the plants in order to flower they require certain day length that is the relative length of day and night which is called as photo period even when we do in vitro cultures of the plants or the plant

00:48:21 tissues or cells we ensure that the optimal photo period is maintained for maximum growth rates to happen in plants so the response of plants to the photo period expressed in the form of flowering is called as photoperiodism in nature so the shoot episodes they'll modify themselves into flowering episodes but they cannot perceive photoperiods so the leaves which are present nearby because they can perceive photo period that is the site of perception of light dark duration which then lead to a hormonal substance

00:49:24 to migrate from the leaves to the shoot episodes for inducing the flowering so this is how the plant regulates the flower bud maturation to flower now depending on the nature of the photoperiod requirements we can classify the plants in three types one as short day plants long day plants and day neutral plants so as you can make out from the term itself the short day plants for example wheat and green gram their growth or their development flowering might be promoted when the light duration is less

00:50:17 however if the light duration is increased or there are flash of lights during the night the dark duration then to you'll observe that the development is affected in terms of flowering in long day plants like for example rice and radish there is a longer duration of photo period which is required and if the photo period or the light illumination period is less then it may impact the flowering again even in that non-illuminated period if there can be flash of lights that may also induce flowering

00:51:12 and in day neutral plants no particular correlation is observed between the exposure to light duration and the induction of flowering response like in case of sunflower or tomato these are examples there is another new term vernalisation which refers to the promotion of flowering by a period of low temperature so let's see how vernalization is useful in certain plant variety like winter variety of wheat plant uses vernalization to complete its growth cycle we know that the plant the seeds are planted during autumn

00:52:24 and then when the winter arises the seeds they mature into small seedlings now during this cold period of growth of the plant from seedling and as it matures the cold temperature effect causes enhancement in or induction in flowering and therefore in spring season you see flowering happening which then subsequently matures and is ready for harvest in the summer season so this low temperature is used by the plant to induce flowering in the growth cycle the plants which follow biennial growth cycle

00:53:16 so even in the plants which follow biennial growth cycle low temperature is used to bring about or to induce flowering in the plant and completing the growth cycle of the plant so the cold treatment in binaural growth cycle also induces flowering or photoperiodic flowering response so in seed dormancy seeds which fail to germinate even when external conditions are favorable in such cases the reasons could be immature embryo or presence of inhibitors like abscisic acid phenolic acid or para ascorbic acid

00:54:21 or the reason could be their impermeable hard seed coat so the measures which are taken to break the seed dormancy either involve removal of the seed barrier by mechanical aberration either through knife or sand paper or abrasion using biological agents like microbes in which they are co-cultured or incubated for some time which will bring about the rupture in the seed barrier or removing the effect of the inhibitory chemicals that is done by subjecting the seeds to chilling conditions which we have learnt now called as

00:55:20 vernalization or by application of antagonistic compounds like gibralic acids or nitrates or changing the environmental conditions like that of light and temperature the photoperiodic response what we studied in plant growth development it included studying the characteristics of plant growth about meri stems the tissues which are responsible for the plant growth we also discussed about the phases of plant growth which included meristematic cells elongation and maturation of the cells then we spoke about essential conditions

00:56:11 needed for the plant growth we discussed differentiation d differentiation and redifferentiation processes we spoke about factors that control the plant development where we studied the effect of plant growth regulators and their functional role we spoke about photoperiodism and vernalization which is responsible in inducing flowering in the plants then we also studied about seed dormancy about its causes and how to prevent so this brings us to the end of the chapter on plant growth and development

00:57:09 [Music] you