Growth, soluble carbohydrates, and aloin concentration of Aloe vera plantsexposed to three irradiance levels

Research was conducted on Aloe vera, a traditional medicinal plant, to inve stigate the effects of light on growth, carbon allocation, and the concentr ations of organic solutes, including soluble carbohydrates and aloin. The p lants were vegetatively propagated and grown under three irradiances: full sunlight, partial (30% full sunlight), and deep shade (10% full sunlight) f or 12-18 months. After 1 year of growth, five plants from each treatment we re harvested to determine total above- and below ground dry mass. Four plan ts from the full sunlight and the partial shade treatments were harvested a fter 18 months to assess the soluble carbohydrate, organic acid and aloin c oncentrations of the clear parenchyma gel and the yellow leaf exudate, sepa rately. Plants grown under full sunlight produced more numerous and larger axillary shoots, resulting in twice the total dry mass than those grown und er partial shade. The dry mass of the plants grown under deep shade was 8.6 % that of plants grown under full sunlight. Partial shade increased the num ber and length of leaves produced on the primary shoot, but leaf dry mass w as still reduced to 66% of that in full sunlight. In contrast, partial and deep shade reduced root dry mass to 28 and 13%, respectively, of that under full sunlight, indicating that carbon allocation to roots was restricted u nder low light conditions. When plants were sampled 6 months later, there w ere only minor treatment effects on the concentration of soluble carbohydra tes and aloin in the leaf exudate and gel. Soluble carbohydrate concentrati ons were greater in the gel than in the exudate, with glucose the most abun dant soluble carbohydrate. Aloin was present only in the leaf exudate and h igher irradiance did not induce a higher concentration. Limitation in light availability primarily affected total dry mass production and allocation, without substantial effects on either primary or secondary carbon metabolit es. (C) 2000 Elsevier Science B.V. All rights reserved.