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Cotyledon Cell Number and Size in Birdsfoot Trefoil

Agric. Stn. of Viseu, Portugal, formerly Dep. of Agronomy, Univ. of Missouri, Columbia, MO 65211
Dep. of Agronomy, Univ. of Missouri, Columbia, MO 65211
USDA-ARS Plant Genetics, Columbia, MO 65211

^* Corresponding author.

Birdsfoot trefoil (Lotus corniculatus L.) has small seed compared with many other forage or grain legumes. Small seed is largely responsible for poor seedling vigor that limits usage of this important forage crop. Factors influencing seed size and cotyledon expansion during seedling growth have not been studied in birdsfoot trefoil. Two studies were conducted to determine if: (i) variation in seed size is due to changes in cotyledon cell number and/or cell size, and (ii) cell division and/or cell enlargement is responsible for cotyledon expansion in growing seedlings. In the first study, cotyledons of MU-81 and ‘Norcen’ birdsfoot trefoil from three seed-size classes were macerated in chromic acid. Cells were counted in aliquots of suspended cells. Cell size was estimated by measuring cell area and by calculating the number of cells per milligram of cotyledon dry mass and the dry mass of an individual cell. Cell number per seed increased by 44 and 50% and cell area increased by 47 and 34% from the small to large seed class in Norcen and MU-81, respectively. In the second study, seeds of MU-81 were germinated and grown in a growth chamber. The number and area of cells in the expanding cotyledons were measured every 4 d for 20 d using methods similar to the first study, except that cotyledons were pretreated with a dilute pectinase solution prior to maceration in chromic acid. Cotyledon expansion was associated with an increase in cell size but not in cell number. Thus, the maximum size an expanding cotyledon could attain was limited by the number of cotyledon cells in a mature seed and their ability to enlarge.

Received for publication March 15, 1989.