Life-Cycle of Plants–Explained !

After reading this article you will learn about the life-cycle of plants.

In plants in which the life-cycle is completed with flowering and subsequent seed formation, conditions during the vegetative stage determine both the size of the machinery for photosynthesis and the number of “sites” (seeds) that will be filled.

Usually there is a good correlation between the size of the plant and the number of seeds initiated, since both are mainly determined by the amount of light energy that has been captured (a certain degree of phenotypic plasticity can be observed here).

High fertility levels tend to favour vegetative growth rather than seed initiation; low radiation levels frequently tend to postpone the onset of flowering and, even more so, seed setting. Both phenomena can be ascribed to the low carbohydrate level prevailing under these conditions.

Therefore, in determinate plants, which complete their life-cycle with seed ripeness, the amount of light intercepted before flowering determines the number of seeds, whereas the amount of light intercepted after flowering determines the total ultimate seed weight, provided no calamities occur in the interval.

Such calamities may cause serious disturbance of the normally rather precise correspondence between the number of flowers and viable seeds. Pollination is a particularly sensitive stage of the life-cycle, and is adversely affected by soil drought or by other soil conditions, such as flooding which induce water deficits.

High air temperatures tend to have adverse effects as well. The success of seed-setting depends mainly on the balance between the levels of reserve carbohydrates and hormones produced by the developing fruits. Thus, in fertile soils or at low light intensities moderate drought may be favourable, since it tends to enhance the carbohydrate content.

In determinate plants, after the onset of flowering, almost the entire dry-matter production is drained into the inflorescences. The first sign that this has started is that root growth is considerably reduced and fairly soon afterwards stops completely. This means that the roots produce less cytokinins and less of these substances is transported to the shoot.

The resulting low cytokinin level in the leaves is the main reason for their senescence, which in turn is accentuated by unfavourable soil conditions. It is clear that the maintenance of a green, light-absorbing surface (leaf-area duration; after seed-setting will determine the mass and possibly also the quality of seeds. Very little is known, however, about the effect of physical soil conditions on seed quality.