College of Agriculture, Bahauddin Zakariya University, Bahadur Sub-Campus Layyah, Layyah, Pakistan.
Cholistan Institute of Desert Studies (CIDS), The Islamia University of Bahawalpur, Bahawalpur, Pakistan.
PLoS One. 2020 May 13;15(5):e0232974. doi: 10.1371/journal.pone.0232974. eCollection 2020.
Heat stress along with low water availability at reproductive stage (terminal growth phase of wheat crop) is major contributing factor towards less wheat production in tropics and sub-tropics. Flag leaf plays a pivotal role in assimilate partitioning and stress tolerance of wheat during terminal growth phase. However, limited is known about biochemical response of flag leaf to combined and individual heat and drought stress during terminal growth phase. Therefore, current study investigated combined and individual effect of terminal drought and heat stress on water relations, photosynthetic pigments, osmolytes accumulation and antioxidants defense mechanism in flag leaf of bread wheat. Experimental treatments comprised of control, terminal drought stress alone (50% field capacity during reproductive phase), terminal heat stress alone (wheat grown inside plastic tunnel during reproductive phase) and terminal drought stress + terminal heat stress. Individual and combined imposition of drought and heat stresses significantly (p≤0.05) altered water relations, osmolyte contents, soluble proteins and sugars along with activated antioxidant defensive system in terms of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX). Turgor potential, POD and APX activities were lowest under individual heat stress; however, these were improved when drought stress was combined with heat stress. It is concluded that combined effect of drought and heat stress was more detrimental than individual stresses. The interactive effect of both stresses was hypo-additive in nature, but for some traits (like turgor potential and APX) effect of one stress neutralized the other. To best of our knowledge, this is the first report on physiological and biochemical response of flag leaf of wheat to combine heat and drought stress. These results will help future studies dealing with improved stress tolerance in wheat. However, detailed studies are needed to fully understand the genetic mechanisms behind these physiological and biochemical changes in flag leaf in response to combined heat and drought stress.
在生殖阶段（小麦作物的终生长阶段），热应激加上低水分可用性是导致热带和亚热带地区小麦产量降低的主要因素。旗叶在小麦终生长阶段的同化产物分配和胁迫耐受中起着关键作用。然而，关于旗叶对终生长阶段的复合和单一热、干旱胁迫的生化响应，我们知之甚少。因此，本研究调查了终生长阶段干旱和热胁迫单独及复合处理对面包小麦旗叶水分关系、光合色素、渗透物质积累和抗氧化防御机制的影响。实验处理包括对照、生殖阶段单独干旱胁迫（50%田间持水量）、生殖阶段单独热胁迫（在塑料隧道内种植小麦）和干旱胁迫+热胁迫。单独和复合施加干旱和热胁迫显著（p≤0.05）改变了水分关系、渗透物质含量、可溶性蛋白质和糖，同时激活了超氧化物歧化酶（SOD）、过氧化物酶（POD）和抗坏血酸过氧化物酶（APX）等抗氧化防御系统。在单独热胁迫下，膨压势、POD 和 APX 活性最低；然而，当干旱胁迫与热胁迫相结合时，这些活性得到了提高。结论是，干旱和热胁迫的复合效应比单一胁迫更具危害性。这两种胁迫的相互作用是亚加性的，但对于某些性状（如膨压势和 APX），一种胁迫的作用会抵消另一种胁迫的作用。据我们所知，这是首次报道小麦旗叶对复合热干旱胁迫的生理生化响应。这些结果将有助于未来研究提高小麦的胁迫耐受性。然而，需要更详细的研究来充分了解旗叶对复合热干旱胁迫的这些生理生化变化背后的遗传机制。
