Singh Rachana, Parihar Parul, Prasad Sheo M
Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad, India.
Front Plant Sci. 2018 Jun 19;9:772. doi: 10.3389/fpls.2018.00772. eCollection 2018.
In the present study, the role of sulfur (KSO: S; 60 mg S kg sand) and/or calcium (CaCl: Ca; 250 mg Ca kg sand) applied alone as well as in combination on growth, photosynthetic performance, indices of chlorophyll fluorescence, nitrogen metabolism, and protein and carbohydrate contents of Indian mustard ( L.) seedlings in the absence and presence of arsenic (NaHAsO.7HO: As; 15 mg As kg sand and As; 30 mg As kg sand) stress was analyzed. Arsenic with its rising concentration negatively affected the fresh weight, root/shoot ratio, leaf area, photosynthetic pigments content, photosynthetic oxygen yield, and chlorophyll fluorescence parameters: the O-J, J-I and I-P rise, Q kinetic parameters, i.e., ΦP, Ψ, ΦE, and PI, along with F/F and Area while increased the energy flux parameters, i.e., ABS/RC, TR/RC, ET/RC, and DI/RC along with F/F and due to higher As/S and As/Ca ratio in test seedlings; however, exogenous application of S and Ca and their combined effect notably counteracted on As induced toxicity on growth and other important growth regulating processes. Moreover, inorganic nitrogen contents, i.e., nitrate (NO) and nitrite (NO) and the activities of nitrate assimilating enzymes, viz., nitrate reductase (NR) and nitrite reductase (NiR) and ammonia assimilating enzymes, viz., glutamine synthetase (GS) and glutamate synthase (GOGAT) along with protein and carbohydrate contents were severely affected with As toxicity; while under similar condition, ammonium (NH) content and glutamate dehydrogenase (GDH) activity in both root and leaves showed reverse trend. Furthermore, S and Ca supplementation alone and also in combination to As stressed seedlings ameliorated these parameters except NH content and GDH activity, which showed an obvious reduction under similar conditions. These findings point out that exogenous application of S and/or Ca particularly S+Ca more favorably regulated the photosynthesis, contents of protein, carbohydrate and inorganic nitrogen, and the activities of nitrate and ammonia assimilating enzymes, which might be linked with the mitigation of As stress. Our results suggest that exogenous application of S+Ca more efficiently defends seedlings by declining As accumulation in root and shoot tissues and by maintaining the photosynthesis and nitrogen metabolism as well.
在本研究中，分析了单独施用以及组合施用硫（K₂SO₄：S；60毫克硫/千克沙）和/或钙（CaCl₂：Ca；250毫克钙/千克沙）对印度芥菜（Brassica juncea L.）幼苗在不存在和存在砷（Na₂HAsO₄·7H₂O：As；15毫克砷/千克沙和As；30毫克砷/千克沙）胁迫下的生长、光合性能、叶绿素荧光指标、氮代谢以及蛋白质和碳水化合物含量的影响。随着砷浓度的升高，砷对鲜重、根/茎比、叶面积、光合色素含量、光合放氧量以及叶绿素荧光参数产生负面影响：O - J、J - I和I - P上升、Q动力学参数，即ΦP、Ψ、ΦE和PI，以及Fv/Fm和Area，同时由于试验幼苗中较高的As/S和As/Ca比值，增加了能量通量参数，即ABS/RC、TR/RC、ET/RC和DI/RC以及F0/Fm和；然而，外源施用硫和钙及其组合效应显著抵消了砷对生长和其他重要生长调节过程的毒性作用。此外，无机氮含量，即硝酸盐（NO₃⁻）和亚硝酸盐（NO₂⁻）以及硝酸盐同化酶，即硝酸还原酶（NR）和亚硝酸还原酶（NiR）以及氨同化酶，即谷氨酰胺合成酶（GS）和谷氨酸合酶（GOGAT）的活性以及蛋白质和碳水化合物含量都受到砷毒性的严重影响；而在类似条件下，根和叶中的铵（NH₄⁺）含量和谷氨酸脱氢酶（GDH）活性呈现相反趋势。此外，单独或组合添加硫和钙对受砷胁迫的幼苗改善了这些参数，但铵含量和GDH活性除外，在类似条件下它们明显降低。这些发现指出外源施用硫和/或钙，特别是硫 + 钙更有利地调节了光合作用、蛋白质、碳水化合物和无机氮的含量以及硝酸盐和氨同化酶的活性，这可能与缓解砷胁迫有关。我们的结果表明，外源施用硫 + 钙通过降低根和地上部组织中的砷积累以及维持光合作用和氮代谢，更有效地保护了幼苗。
