Nuclear Research Laboratory, Indian Agricultural Research Institute , New Delhi , India.
Int J Radiat Biol. 2014 Feb;90(2):179-86. doi: 10.3109/09553002.2014.868615.
An experiment was carried out to determine the effect of low dose gamma radiation on germination, plant growth, nitrogen and carbon fixation and carbon flow and release characteristics of groundnut.
Dry seeds of groundnut variety Trombay groundnut 37A (TG 37A), a radio mutant type developed by Bhabha Atomic Research Centre (BARC), Mumbai, India, were subjected to the pre-sowing treatment of gamma radiation within low to high dose physiological range, i.e., 0.0, 0.0082, 0.0164. 0.0328, 0.0656, 0.1312, 5, 25, 100, 500 Gray (Gy) from a cobalt source ((60)Co). Observations were recorded for the radiation effect on percentage germination, vigour, gas exchange attributes such as photosynthetic rate, stomatal conductance and transpiration rate, chlorophyll content, root exudation in terms of (14)C release, vascular sap flow rate and activities of rate defining carbon and nitrogen assimilating enzymes such as ribulose-1,5-bisphosphate carboxylase (rubisco) and nitrate reductase (NR).
Seed germination was increased by 10-25% at the lower doses up to 5 Gy while the improvement in plant vigour in the same dose range was much higher (22-84%) than the unirradiated control. For radiation exposure above 5 Gy, a dose-dependent decline in germination and plant vigour was measured. No significant effect was observed on the photosynthesis at radiation exposure below 5 Gy but above 5 Gy dose there was a decline in the photosynthetic rate. Stomatal conductance and transpiration rate, however, were only inhibited at a high dose of 500 Gy. Leaf rubisco activity and NR activities remained unaffected at all the investigated doses of gamma irradiation. Mean root exudation and sap flow rate of the irradiated plants, irrespective of the dose, was reduced over the unirradiated control more so in a dose-dependent manner.
Results indicated that a very low dose of gamma radiation, in centigray to gray range, did not pose any threat and in fact stimulated metabolic functions in such a way to aid growth and development of groundnut plants. It further showed that the radiation threshold for the gas exchange traits and rubisco activity, which ultimately determine the plant health and yield, were higher than compared to the other metabolic attributes and were well beyond 500 Gy and that the dose range above 500 Gy should be targeted to measure lethal effects of radiation on carbon assimilation attributes in leguminous crops, in general, and groundnut in particular.
本实验旨在研究低剂量伽马辐射对花生萌发、植物生长、氮碳固定以及碳流动和释放特性的影响。
选用印度孟买巴巴原子研究中心（BARC）培育的突变型干花生种子——Trombay 花生 37A（TG 37A），对其进行不同生理剂量范围（0.0、0.0082、0.0164、0.0328、0.0656、0.1312、5、25、100、500 戈瑞）的预播种伽马辐射处理，辐射源为钴（60）Co。记录了辐射对种子发芽率、活力、光合作用相关气体交换特性（如光合速率、气孔导度和蒸腾速率）、叶绿素含量、14C 释放量的根系分泌物、维管束汁液流速以及决定碳氮同化酶（如核酮糖-1,5-二磷酸羧化酶（Rubisco）和硝酸还原酶（NR））活性的影响。
种子发芽率在低剂量（0-5 Gy）下提高了 10-25%，而在同一剂量范围内，植株活力的提高幅度（22-84%）远高于未辐照对照。当辐射剂量超过 5 Gy 时，发芽率和活力都呈剂量依赖性下降。在 5 Gy 以下的辐射暴露下，光合作用没有明显影响，但在 5 Gy 以上的高剂量下，光合速率下降。然而，只有在 500 Gy 的高剂量下，气孔导度和蒸腾速率才会受到抑制。叶片 Rubisco 活性和 NR 活性在所有研究剂量的伽马辐照下均不受影响。无论剂量如何，辐照植株的平均根系分泌物和汁液流速均低于未辐照对照，且呈剂量依赖性降低。
结果表明，低剂量伽马辐射（在百分格雷至格雷范围内）不会造成任何威胁，实际上还以促进生长和发育的方式刺激代谢功能。这进一步表明，用于确定植物健康和产量的气体交换特性和 Rubisco 活性的辐射阈值高于其他代谢特性，并且远高于 500 Gy，而在 500 Gy 以上的剂量范围内，应该测量辐射对豆科作物，特别是花生的碳同化特性的致死效应。
