Abstract
BackgroundEarlier we have reported that the exclusion of solar UV-B increased the growth and yield of cotton plants as compared with ambient UV-B. The UV-B radiation effects on the saponins and the impact of ambient and reduced UV-B on the accumulation of saponins has not been investigated yet. Thus a field experiment was conducted to study the influence of solar UV-B on the growth response and saponin synthesis in cotton (Gossypium hirsutum) var. Vikram plants by the exclusion of UV-B. The cotton plants were grown in specially designed iron chambers, wrapped with filters that excluded UV-B (<315 nm), or transmitted ambient UV-B.ResultsExclusion of ambient UV-B enhanced the growth of cotton plants in terms of plant height and leaf area. Greater plant height in UV-B excluded plants was due to elongated internode and more number of nodes. Enhancement in growth was accompanied by a decrease in the accumulation of saponins, which was quantified by the spectrophotometric, TLC and HPLC methods. Solvent extraction of saponins from the internodes and leaves were used for the bioassay of Amaranthus hypocotyl growth and expansion of cucumber cotyledons. Extracts obtained from the UV-B excluded plants (leaves and internodes) promoted the growth to a larger extent as compared with the extracts obtained from ambient grown plants.ConclusionsThe result indicates that solar UV-B may possibly suppress the plant growth by regulating the synthesis of natural growth inhibitor’s like saponin.
Highlights
Ultraviolet (UV)-B radiation (280–315 nm) is a natural component of sunlight
UV exclusion and growth Cotton plants grown under UV-B exclusion filters for 70 days after emergence (DAE) showed an enhancement in the height of the plant and in the area of leaf (Fig. 3)
The HPLC separation of fractions of the leaf extracts of cotton plants showed a significant quantitative difference between the extracts obtained from filter control plants and the UV-B excluded plants at the Retention time = 3.23 (Fig. 6, Table 2) compared with similar band of the standard
Summary
Ultraviolet (UV)-B radiation (280–315 nm) is a natural component of sunlight. The amount of UV-B radiation reaching the Earth’s surface has increased over the last decade due to ozone depletion (Caldwell et al 2003; McKenzie et al 2011). Crop plants grown under tropical conditions receive approximately 50% higher dose of UV-B in the natural solar radiation compared. Saponin-triterpenoid glycosides are one of the most interesting groups of secondary metabolites. The saponins are a group of plant glycosides in which hydrophilic sugars are attached to alipophilic steroid or triterpenoid moiety. The growth inhibitory effects of triterpenoids saponins have been shown earlier using alfalfa seeds (Ohara and Ohira 2003). Three triterpenoids (betulin, betulinic acid and oleanolic acid) inhibited radical and hypocotyl growth in alfalfa seeds (Ohara and Ohira 2003). Earlier we have reported that the exclusion of solar UV-B increased the growth and yield of cotton plants as compared with ambient UV-B. The cotton plants were grown in specially designed iron chambers, wrapped with filters that excluded UV-B (
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