Erica's Original Notes Hormones are subtle substances that control and direct plant messages used to trigger certain functions. Animal hormones are produced by special organs or glands, with specific effects; plant hormones are produced in fairly restricted regions but are manufactured by unspecialized cells, with many different effects depending on circumstances, usually at a site other than its place of origin.
Auxinsare growth hormones which are found in the growing tip of a plant. These cells are undifferentiated/permanently embryonic meristematic cells; they are responsible for the beautiful symmetry of a tree, and when the leader deviates from the vertical, as may happen on a slope, the auxins will accumulate on the underside, thus enlarging the cells, to correct this position. Cutting the leader of a plant will stimulate the side shoots to grow with increased hormonal activity. Auxins also work to stimulate the growth in roots; gardeners often use rooting powders in order to get cuttings to take. In phototropism, we find that because auxins are broken down by light, the plant will lean towards it, while the cells on the shady side enlarge. Seeds produce auxins which go into the surrounding tissue; if pollination is uneven, the resulting fruit will be misshapen or there is a June 'drop': if an apple has less than 10 seeds, it will drop. Fruit growers may spray their crops with hormone to increase their crop.
Kinetinappears in ratio with auxin and promotes orderly growth and bud formation; it can also prevent nutrients moving out of the old leaves.
Gibberellic acidwas discovered in 1950 and elongates plant cells; it is responsible for the 'foolish rice' disease in Japan that causes rice to grow too rapidlyt is used to promote stem growth in tree fuchsias; it also breaks seed and bud dormancy.
Cycocel is a commercial product inhibits gibberellic acid and retards growth.
Abscissic acidwas formerly known as Dormin which accumulates in over-wintering buds and inhibits their opening until cold has broken down the hormone, for example, lilacs, unless subjected to cold weather, will not open their buds, and are not, therefore, good subjects for forcing. This hormone is also found in seed coats and inhibits germination. It also controls the loss of water by closing the guard cells of the stomata. It is used by the Nursery Trade in order to get deciduous trees to drop their leaves quickly, so that they can be dug up and put in cold storage before the rains start.
Ethylene is a plant hormone that affects almost every aspect of its growth: seed germination, cell growth, shoots, flowers and ripening of fruit. If fruit is bruised it gives off more ethylene and promotes 'ageing' of fruit and it will wilt nearby flowers; for this reason in agricultural shows, fruit displays are situated a long way from the flower exhibits! If you bring your lunch bag containing an apple to your work at the florist's shop, you will not be allowed to put it in the cooler with the flowers! However, conversely, if you wish to hasten the ripening of fruit, putting it in a bag with apples will do the trick.
Florigenis manufactured in the leaves and is used in the promotion of flowering.
Carotenoids (Pigments) and Riboflavin (Vitamin) are both involved with animal vision, and, in plants, may be active in the reaction to light.
Hormones are used to promote quick flowering, e.g. in pineapple; to stop bolting in celery and lettuce; to control growth; and as an aid in transplanting.
Experiments: In Dehra Dun in India, Dr. Chandra Bose experimented to show that plants have a nervous system. He chloroformed a tree in full leaf, and transplanted it successfully.