Dormancy and suvival PHYSIOLOGY of plants

0
12

DORMANCY AND SURVIVAL PHYSIOLOGY OF PLANTS

BY GHULAM MOHYUDDIN WANI AND KALEL JEBRAN WANI

Mancy Trees have five major phonological stages: Start, leaves, growth, storing and rest. Reproduction is a sub-pattern that usually starts near stage two. It is impossible to generalize these patterns because there are almost as many variations as there are species. However, every tree system must start again from a quiet period. Every tree must produce new leaves or needles for photosynthesis. Every tree must increase in mass; this is growth. Every tree must store ingredients essential for survival. Every system must rest. Most trees also have reproductive cycles. Some are extremely complex in their patterns DORMANCY Dormancy is usually thought of as a period of rest where processes essential for life function at a minimal rate. Dormancy does not mean stopping! Stopping is death. The second law of thermodynamics states that no system will survive unless it receives a continuous supply of energy to maintain order. In order to survive, trees must also have a supply of water and essential elements. Tree as a composite system Trees are often referred to as living systems. Many of the problems with understanding phonological stages could be clarified if a tree was viewed not as a single system, but rather as a cluster of systems connected many aboveground stages are different from those belowground.

PHYSIOLOGY OF PLANT DORMANCY

Physiology Plants even during dormancy need energy. This energy is stored in the plant. Let see how it happens. First PLANTS form ATP, which is used to form glucose which then forms cellulose, starch and a great number of other substances. Still, glucose is the fuel that makes it possible for the tree to survive. Trees do have ways of storing energy reserves and for regulating the use of the energy for processes to survive even during dormancy.. Second requirement is water. We think of water, mostly, in its liquid form. Water molecules enzymatic ally removed or inserted are essential for many processes and products, from cellulose to starch and back to glucose. Trees store water as bound water on the hydroxyls on cellulose. The water is bonded to the cellulose by very weak, but significant, hydrogen bonds. When any force greater than hydrogen bonds is exerted, the bound water then moves to liquid water again. Water can also exist as a gas or as a solid. As temperatures decrease, the constantly changing positions of the water molecules slow, and if the constantly changing positions of the water molecules slow, and if temperature continues to decrease, all possible positions for hydrogen bonding will be occupied and molecular motion stops – ice formation. This seems to be a possible way of water flow during dormancy. WHY TROPICAL PLANTS DIE IN COLD Water and energy flow downhill, or from high concentrations to lower concentrations. When ice forms in the spaces between cell walls and even in cell walls, liquid water flows out of the cell and death from dehydration usually follows in plants that are not cold hardy. But if ice does not form, then dehydration may not occur. When temperatures decrease below 0 degrees Celsius, and the water is pure and quiet, ice may not form. This is called super cooling of water. STORAGE OF ESSENTIAL ELEMENTS Elements in molecules often precipitate when pH increases. This we know for iron, manganese and other elements. We know also that some elements such as potassium can be bonded in many cheated-like forms. Potassium is an element that is absorbed in its pure form. When potassium is in high concentrations, the electrical resistivity (as measured by a Shigometer) of the wood is very low. In summer during the growing season, electrical resistivity in k-Ohms is low. As winter approaches, the electrical measurements increase greatly. Summer could be in the 8 k-Ohm or 10 k- Ohm range while winter could be in the range of a hundred, or even higher. If potassium is a factor in electrical resistivity, then it must be bonded in ways that prevent its action as an electrolyte. Mycorrhizae are active in cold The mycorrhizae are not only in no frozen soil under frozen soil, but from soil under water that was covered by ice. Further, many of the mycorrhizae and root hairs at 1,OOOX with a phase microscope showed abundance of hyphae inside the non-woody roots. The nucleus in a root hair is at the tip of the cell. Nuclei in all shapes were viewed. Active nuclei are round and as they age and die, they become spindle-shaped. ADAPTATION PROCESS it is not difficult to expect processes of some long-term systems optimizing places and conditions considered not the best for life. Absorption of elements developed or adjusted to low temperatures. This then extended the time for a larger cluster of systems to survive. Trees have always been and still are the most massive, tallest, longest living organisms on Earth. To be such superior survivors without the benefits of movement, the tree systems adapted and adjusted to every possible condition present over a period of one solar year. Absorption Mycorrhizae are organs made up of fungus and tree tissues. The organs facilitate the absorption of water and elements essential for healthy growth. Trees have many redundancies, some for short-term conditions and some for long-term conditions. Root hairs are finger-like extensions of single epidermal cells that contain very little lignin in their walls. The cell walls of the epidermis do have cellulose, which is not the best of boundaries or membranes for absorption of water and elements. Root hairs are usually ephemeral. They grow as new roots grow and they go or die as woody roots begin to form a bark that contains suberin. Their numbers are usually so great that even if they are poor absorbing structures, they still absorb some water and elements. Mycorrhizae present a system of synergy. The fungi receive more and the tree receives more with this association. Mycorrhizae live for long periods; a year or more. (Note forms that bud.) | A mycorrhiza starts when a hypha from a germinating spore infects a newly forming non-woody root. When some fungi infect a root, they control the further development of that root. Some fungi penetrate the root and hyphae spread far beyond the root. It is not uncommon to see some mycorrhizae with hyphae completely wound about the organ. Root hairs do exist on some mycorrhizae. The question quickly arises about how fungi can exist in roots in soil under water. To make sure the roots were from neighbouring trees, samples were collected from streams where only one tree species was growing. Large woody roots with smaller masses of roots were dug. The mycorrhizae were on the tree roots, mostly Acer rubrum and Ulmus americana. The fungi in roots under water appeared typical for species close to Glomus – a member of the Zygomycetes. Chlamydospores of several types were abundant from the winter samples. (The organisms in the roots could be oomycetes, which are close to water molds. If this can be shown, then the organisms would be better classified as endophytes. There is so much yet to be learned.)

Source by G.M. Wani

Loading...