ENVIRONMENTAL-EFFECTS ON SEED DRY-WEIGHT AND CARBOHYDRATE-COMPOSITIONAS RELATED TO EXPANSIVE GROWTH OF CUCUMBER (CUCUMIS-SATIVUS L) FRUIT

Cucumbers ('M-27'), planted into 11-1 pots, were cultured outdoors unt il anthesis. During fruit development, plants were exposed to nocturna l temperature treatments of 12-29 degrees C by transferring them into dark constant temperature rooms from 20:00 to 08:00 h the next day. Ot her treatments imposed during fruit development included drought stres s, the withholding of water until predawn leaf water potentials reache d -0.6 MPa, and 50% full sunlight by placing plants under a canopy of plastic netting. Expansive growth rates of cucumber fruit, as measured by changes in fruit diameter, were most rapid under high nocturnal te mperatures (24 or 29 degrees C), full sunlight and regular irrigation. Seeds with the highest dry weights were extracted from 5.1 cm diamete r fruit which developed under high nocturnal temperatures, the combina tion of high nocturnal temperature plus 50% full sunlight, or under dr ought stressed conditions. The concentrations of sucrose, fructose and glucose were significantly lower, while raffinose was higher in seed tissues from the treatments which resulted in the highest seed dry wei ghts. High nocturnal temperatures, 24 degrees C or higher, resulted in a depletion of stachyose and sucrose concentrations within phloem sap collected from excised peduncles, 1 h after transfer into the light, compared with the 12 or 15 degrees C nocturnal temperature treatments.