DIURNAL FLUCTUATION OF CARBOHYDRATE CONCENTRATION OF YOUNG WATERMELON PLANTS AS AFFECTED BY LIGHT QUALITY

Abstract

Young watermelon (Citrullus lanatus cv. Sugar Baby) plants were treated with end-of-day (EOD) Red (R), Far-red (FR), and Far-red followed by Red (FR/R) light for 15 minutes. Control plants had no EOD light treatment. FR light treatments influenced plant growth and development (i.e., petiole elongation, internode elongation, and reduced petiole angles). Plants were sampled every 4 hours for a 24 hour period from each light treatment. Tissues (petioles, leaves, stems, and cotyledons) were analyzed from each treatment and sampling time combination for soluble carbohydrate and starch concentrations. Results suggested that carbohydrate concentration, distribution, and diurnal fluctuation were affected by EOD light quality treatments. Petioles of FR treated plants contained the greatest concentration of glucose, fructose and total soluble carbohydrates, and the least concentration of stachyose and starch. Stems of FR treated plants had the least concentration of total sugars and starch. Petioles of R treated plants contained the greatest concentration of stachyose and the least concentration of glucose. The changes in concentration of the storage carbohydrate (starch) and breakdown products (fructose and glucose) of the translocated sugar (sucrose) may be correlated to active growth of petioles and stems in response to light quality.