Time Of Floral Initiation Research Articles

Change in Carbohydrates in Alfalfa (Medicago sativa L.) Roots During the Period of Floral Initiation and Seed Development1

Alfalfa plants grown under field conditions at Tucson, Arizona, were used to investigate the change in acidhydrolyzable carbohydrates, glucose, fructose, sucrose, and starch stored in the roots during the time of floral initiation and seed development at three different seasons of the year.Acid‐hydrolyzable carbohydrates and starch reached their lowest level in the roots more rapidly in plants that were cut in June and August as compared with plants that were cut in April to begin growth for seed production. Floral initiation and development also occurred earlier during the June and August growth periods. This early reduction in stored reserves coincided with early floral initiation and development. The concentration of glucose, fructose, and sucrose was quite low in alfalfa roots during all growth periods. Positive and significant association existed between the concentration of specific carbohydrate fractions in alfalfa roots during the first three weeks after forage removal and seed production, number of pods per stem, number of seeds per pod, and percentage pod set.

A COMPARATIVE DEVELOPMENTAL STUDY OF THE MUTANT SIDESHOOTLESS AND NORMAL TOMATO PLANTS

'Sideshootless,’ a mutant strain of tomato which does not produce axillary buds during vegetative growth, was compared with normally branching plants in order to study the nature of development particularly with regard to axillary buds. Sectioned material revealed no indication of axillary bud initiation in the sideshootless plant at any time during the vegetative phase of growth. In the normal plants, buds were noted to arise in the axil of the fifth youngest leaf. The buds take their origin in tissue which is in direct continuity with the apical meristem. The bud primordia later become set apart from the apex as vacuolation takes place in the surrounding tissue. At the time of floral initiation, the mutant and normal strains behave similarly. Axillary buds appear in the axils of the 2 leaves immediately below the floral apex. One of the buds elongates to overtop the existing plant axis; the other develops as a typical sidebranch. The inflorescence is pushed aside in the process. This pattern is repeated with each inflorescence; thus an axis composed of several superimposed laterals results.

CONTROL OF CHLOROPHYLL CONTENT BY DAYLENGTH IN LEAVES OF MARQUIS WHEAT

The maximal chlorophyll contents reached during the growth of each of the first three leaves of Marquis wheat increased linearly with daylength, when the plants were grown from germination under illumination of 1750 ft-c intensity for daily periods of 8, 16, or 24 hours. This effect of daylength was also seen when chlorophyll concentration was expressed on a unit leaf area or fresh weight basis, and was related to increased leaf thickness at the longer daylengths. The increased chlorophyll content and concentration under long daylengths could not be duplicated by extending short daylengths with low-intensity supplementary light. Previous experiments suggest that the control of chlorophyll content by daylength is through the control of leaf thickness by the total amount of daily energy.The ratio of chlorophyll a to b in mature leaves did not vary with daylength. There was also no change in the maximal chlorophyll concentration of leaves mature at the time of floral initiation compared with those mature in the vegetative stage of development.