Leaf and Tiller Growth

John Guretzky, Amy Kohmetscher, and Deana Naumuth-Covert Author

05/10/2019 Added

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The growth of grass leaves and tillers.

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[00:00:00.400]Hi, I'm John Guretzky from the University of
[00:00:03.166]Nebraska.
[00:00:04.400]Today I'm going to talk to you about growth of grass, leaves and tillers.
[00:00:10.680]Before I begin, I would like to acknowledge that
[00:00:14.031]development of this lesson was made possible by a grant from the USDA NIFA
[00:00:19.160]AFRI program on Sustainable bioenergy.
[00:00:23.360]Growth of grasses is typically recognized by agronomists at the whole plant and
[00:00:28.898]canopy levels as an increase in plant dry matter.
[00:00:33.600]In reality, growth is a complex interaction of
[00:00:37.307]physiological processes, including photosynthesis, respiration,
[00:00:42.356]mineral nutrition, and water relations that occur at the
[00:00:46.852]cellular to organismal levels of organization.
[00:00:53.520]Growth proceeds in regions of cell division and enlargement known as
[00:00:59.140]maristems, apical mare stems located at the tips of
[00:01:03.376]stems and roots.
[00:01:05.080]These cylindrical columns of roots and stems behind.
[00:01:09.800]As new cells are produced, the mare stems perpetuate themselves by
[00:01:14.880]maintaining a small population of undifferentiated dividing cells.
[00:01:21.080]Each time a cell divides, a doner is left behind to elongate and
[00:01:25.886]move the apex forward while the other remains within the meristem to continue
[00:01:31.654]dividing.
[00:01:35.120]Cells elongate and differentiate as distance from the apical meristem
[00:01:40.230]increases.
[00:01:42.000]This figure depicts cell development as a function of distance from the meristem.
[00:01:48.280]Notice at the bottom of this figure you see a distance ranging from zero to 15mm,
[00:01:55.477]so 1. 5 centimeters within the region closest
[00:01:59.515]to the meristem.
[00:02:01.080]Within that zero to 5mm region, that is the area or the zone of cell
[00:02:06.352]division.
[00:02:07.720]You can see in this figure 2 cells.
[00:02:11.000]As you move further out from that chute or root tip into say 5 to 10mm away,
[00:02:17.554]you have the region of cell enlargement.
[00:02:21.640]Here cells begin to enlarge by growth of the vacuole within that cell and uptake
[00:02:28.829]of water further on out.
[00:02:31.320]Between 10 to 15mm those cells begin to differentiate and you begin to see sub
[00:02:38.566]cellular organelles develop as that cell specializes.
[00:02:43.840]Here you may see chloroplasts as well as mitochondria and other subcellular
[00:02:48.941]organelles.
[00:02:53.560]This next figure depicts growth of the chute apical meristem at the tiller level
[00:02:59.473]of plant organization.
[00:03:02.320]Labeled on this figure are morphological structures including the chute apical
[00:03:09.304]meristem leaves, intercalary meristems, and axillary buds.
[00:03:16.480]The chute apical meristem has several functions that are worth noting as the
[00:03:22.434]tiller grows.
[00:03:23.440]As a grass tiller grows, cells formed by the shoot apical marrow
[00:03:28.983]stem differentiate into buds or into primary primordia.
[00:03:34.320]Or primordia are the beginnings of say, new organs such as leaves, axillary buds,
[00:03:41.325]and the floral parts.
[00:03:45.000]So apical meristem cells differentiate into, say, leaf primordia.
[00:03:50.800]Leaf primordia give rise to the leaves.
[00:03:55.000]Those apical meristem cells may differentiate into axillary buds.
[00:04:00.200]You can see the axillary buds here, located in these round structures between
[00:04:05.730]the axis of a leaf and the stem.
[00:04:08.600]These axillary buds will actually give rise when they develop into a new tiller
[00:04:15.746]or a new grass shoot. Intercalary meristems noted on this
[00:04:20.927]figure at the base of this internode, we're right above a node or this area
[00:04:27.716]marked with with the dark shading here.
[00:04:31.800]These intercalary meristem are responsible for elongating that stem.
[00:04:41.400]This next slide provides another depiction of the shoot apical meristem,
[00:04:46.757]its leaves, axillary buds, and intercalary meristems.
[00:04:51.600]The intercalary meristems are labeled with the letters A, B and C.
[00:04:57.480]Looking at letter A, that's depicting an intercalary meristem
[00:05:01.504]that occurs at the base of that leaf blade.
[00:05:05.800]Cell division and elongation in this meristem will then give rise to the long
[00:05:11.964]linear growth characteristic of grass blades.
[00:05:16.920]The overall size of the blade and the rate that it elongates is impacted by
[00:05:22.214]environmental factors such as water and nutrient deficiencies that effect rates
[00:05:27.787]of cell division and elongation within the meristem.
[00:05:32.920]Letters B and C depict the intercalary meristems that are responsible for the
[00:05:40.637]leaf sheath and the stem elongation.
[00:05:48.280]The cell division and elongation zone of a developing leaf blade is located within
[00:05:54.677]the world of older existing leaf shoots.
[00:05:58.880]Location with of that growing point within these older leaf shoots provides
[00:06:04.692]some protection to that developing leaf blade in those functional growth zones
[00:06:10.734]from disturbances such as defoliation or herbivery as well as adverse
[00:06:16.088]environmental conditions.
[00:06:18.680]For instance, growing, grazing or mowing of this grassland plant
[00:06:23.499]canopy tends to only remove these mature leaf blades at the top of the canopy,
[00:06:29.357]leaving intact this functional growth zone that can rapidly restore both an
[00:06:34.992]existing leaf in that plant canopy as well as development of new tillers.
[00:06:43.080]The cell division and elongation zones of a leaf are sites of high dry matter
[00:06:48.805]accumulation.
[00:06:50.440]Dry matter accumulation is mainly in the form of water soluble carbohydrates and
[00:06:57.086]proteins, but these regions also serve as sinks for
[00:07:01.353]potassium, magnesium, and other nutrients.
[00:07:06.400]This graphic depicts a leaf blade and the cellular processes that occur with
[00:07:12.478]distances along that blade as it develops within a whorl of older leaves.
[00:07:19.600]The overall blade may be 100mm long within the zero to 10mm region at the
[00:07:26.474]base of that blade.
[00:07:28.920]Cell division occurs from that region of 10 to 30mm.
[00:07:35.160]These cells that had divided begin elongation and begin accumulation of
[00:07:40.577]those water soluble carbohydrates in nitrogenous compounds imported from
[00:07:46.069]elsewhere in the plant.
[00:07:49.240]The carbohydrates then in proteins then are utilized in the region,
[00:07:54.521]say from 30 to 60mm for development of chloroplasts,
[00:07:58.638]photosynthetic pigments and photosynthetic enzymes such as Rubisco.
[00:08:05.480]As that leaf matures, carbohydrates then provide energy and
[00:08:09.971]carbon skeletons for secondary cell wall formation in nitrogen is recycled for
[00:08:15.884]photosynthetic proteins as well.
[00:08:19.600]Mature cells in a leaf continue to differentiate and accumulate biomass as
[00:08:25.455]that leaf transitions then from being a carbon sink to actually being being a
[00:08:31.544]carbon source for new leaves that develop within the world of that canopy.
[00:08:40.720]Leaf and tiller emergence are synchronized in grasses.
[00:08:46.200]Each bud produced in a leaf axil has potential to develop into a new tiller.
[00:08:52.920]The following table outlines a repeated developmental sequence of leaves and
[00:08:59.138]tillers that has been observed on tall fescue, a forage, and turfgrass species.
[00:09:07.120]The cotyledon is located at node one, and the coleoptile of the grass is
[00:09:12.350]located at node 2.
[00:09:14.280]Leaf 1 develops at node 3, and thus leaf #2 develops at node 4.
[00:09:22.000]This table depicts this developmental sequence from nodes 4 through 7 sequence
[00:09:28.721]here's lifted in this left hand column.
[00:09:32.360]So in order then at node 4, if you look at what's occurring at node 4
[00:09:38.073]in sequence one is division in the leaf sheath of that second leaf is ending.
[00:09:45.120]Followed after that you start to get elongation of the axillary bud or the
[00:09:50.798]tiller within that axillary bud at the base of that leaf sheath.
[00:09:58.440]The third sequence begins at node 5. So node 5 is a younger node and at that
[00:10:06.079]node initiation of the ligule on leaf 3 is beginning at node 6A yet younger node
[00:10:14.116]elongation is beginning for blade of leaf #4.
[00:10:20.240]Notice how these developmental steps then repeat themselves like sequence one.
[00:10:26.480]Sequence 5 is similar, but it's now the the third leaf division
[00:10:31.582]in the leaf sheath of the third leaf is ending,
[00:10:35.409]then elongation of its tiller begins.
[00:10:39.880]Subsequently, the ligule then is initiated on leaf
[00:10:45.398]blade #4 and then at node 7 elongation begins for blade 5 as the process repeats
[00:10:54.162]itself.
[00:11:01.960]Grass tillers themselves are often diagrammed as consisting of phytomers.
[00:11:06.760]To illustrate this overall synchronized development of leaves and tillers,
[00:11:12.453]this figure depicts a reproductive tiller consisting of four phytomers.
[00:11:18.920]A phytomer is a repeating unit of growth that consists of a node, an internode,
[00:11:25.661]a leaf blade, a leaf sheath, and an axillary buds.
[00:11:30.400]So you can see in this figure how this overall tiller is broken up into each of
[00:11:35.343]those phytomers, and you can see the space between each
[00:11:38.803]phytomer.
[00:11:40.360]So each of those phytomers then again consists of the node, its internode,
[00:11:45.593]the leaf sheath that surrounds that internode, the blade.
[00:11:49.760]And then what you can't see here is that that axillary bud that would occur at the
[00:11:54.575]base of each of those nodes.
[00:11:58.720]Overall, this phytomer production then ceases once
[00:12:03.060]the apical maristem is induced to be reproductive.
[00:12:09.240]Reproduction within a grass tillers in temperate grasses is typically triggered
[00:12:14.317]by changes in day length and temperature.
[00:12:19.880]That wraps up this lesson.
[00:12:22.360]My hope is that you formed a greater appreciation in understanding of how
[00:12:27.475]grass, leaves and tillers grow, and ultimately you may use this
[00:12:31.900]information to improve management of grasses.

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Leaf and Tiller Growth

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