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Gross Morphology and Starch Accumulation in Leaves of Alfalfa Plants Grown at High and Low Temperatures¹

Studies have shown that leaves of alfalfa (Medicago sativa L.) plants grown at cool temperatures accumulate more starch than those grown at warm temperatures. The present study was initiated to observe more closely the influence of temperature on leaf development. Plants were grown to first flower at 21/12, 32/24, and 30/30 C day/night temperatures. Leaflet anatomy, and concentration and location of starch grains were observed in fully-expanded, upper leaves, and measurements of leaf area, dry weight, and carbohydrate composition were made.

Upper leaves grown at 21/12C were heavier and larger and had a greater specific leaf weight than those grown at 92/24 or 30/30 C. Leaves grown at 21/12 C contained high amounts of starch at first flower; 40.3% as compared with 6A% at 32/24 C and 12.9% at 30/30 C. Starch grains were confined to chloroplasts. Chloroplasts were distinct in the high-temperature leaflets, but they could not be identified readily in cool-temperature leaflets because of the high starch accumulation. Palisade cells were more compact at cool temperatures than at warm temperatures.

Key Words: Leaf weight • Leaf area • Specific leaf weight • Leaf carbohydrates • Leaflet anatomy

² Professors of Agronomy and Horticulture, respectively, University of Wisconsin, Madison, WI 53706. The helpful assistance of P. L. Greenfield is gratefully acknowledged.

Received for publication October 5, 1973.