رشد، رنگيزه هاي برگ و فتوسنتز گياه شلغم (.Brassica rapa L) تحت كمبود بور و شدت هاي مختلف نور

Growth, leaf pigments and photosynthesis in boron-deficient turnip (Brassica rapa L.) plants under different light intensities

Effect of boron deficiency on growth, leaf pigments and photosynthesis was studied in turnip {Brassica rapa L.) plants grown under three different light conditions (50, 100 and 150 (imol m-2 s"1) in a hydroponic medium for one month under controlled environmental conditions. Two levels of B treatment including adequate (25 |liM) and low (2.5 \iM) boron supply were applied. Dry matter production of shoot and root was reduced under low boron supply up to 79% and 82% respectively. Re- supply of deficient plants by boron during the last week of growth period increased significantly plants dry matter production. Higher light conditions increased not only plants growth but also boron uptake. Plants susceptibility to low boron supply was higher under high compared with lower light conditions. Leaf chlorophyll and carotenoids decreased under boron deficiency conditions while leaf anthocyanins and free soluble phenolics in leaf and roots increased in low boron plants. Boron deficiency did not cause impairments of photochemical events in leaves, however, stomatal conductance was reduced strongly in low boron plants that caused reduction of net CO2 assimilation rate and transpiration. Though reduction of net assimilation rate, soluble sugars and starch were accumulated in boron deficient leaves and roots that was likely the result of lower phloem loading of assimilates and lower use due to growth inhibition respectively.