Abstract
Alginate oligosaccharides (AOS) are known for functions in regulating plant growth and stress resistance. This study investigated the damage on rice leaves caused by acid rain (AR) and high temperature (HT) simultaneously, as well as the alleviating effect of AOS on these stresses. The results show that plant biomass and antioxidant enzyme activities (AEAs) after AR treatment reduced more severely under HT conditions than normal-temperature conditions. Both AR and HT triggered the accumulation of reactive oxygen species (ROS) in rice leaves. The suppressing effects of AR and HT were individual in most cases, except for AEAs. Microscopic analysis showed that pH 2 AR and HT injured leaf epidermis, particularly the bulliform cells, the veins and interveinal regions. Spraying AOS resulted in a slight elevation of biomass, a significant increase in AEAs and a remarkable decline in ROS concentrations under HT conditions with AR. Besides, the chlorophyll a contents of a leaf after pH 2 AR plus AOS treatment under HT conditions remained 66.1% of that after pH 7 treatment under normal-temperature conditions. Moreover, AOS protected the integrity of leaf tissue even after pH 3 treatment. Taken together, the above results suggest that AR and HT inhibited AEAs, led to the accumulation of ROS and damaged rice leaf. However, foliar applying AOS enhanced AEAs, scavenged ROS, and thus alleviated the stress induced by HT and AR.
Highlights
The deleterious effects for crop production often originate from several ambient stresses occurring simultaneously [1]
Accompanying structural damages in the plasma membrane and chlorophyll, CO2 accumulates in intercellular space due to narrower stomata after exposure to acid rain whose pH was lower than pH 3, and the rate of photosynthesis is lowered [13]
Longituddioneasl sneocttioinnds uofcericdealmeaavgees tsrpeaottesd[1w0i]t.hHdioffwereevnet rp,Hstraocindgraaicnidwritahinan(pdHwi2th)‐triggered excessive Totuuhrteefltoerlaeiavartemsapseupnbtly.je(inact,gefOidA)rr2TtOe−ohvSe·nefoalroesrnramidbv7aeldHelsatiw2eynOmsijtu.h2pIrneaytrhjcuasecrtyuuycmormsenpputtorrtlotoeasalmtti(inmposHtne(hFnei7tin.)gle(turfrai‐refcjea)bestTlmal6hedeeaanevnltew.eda(sevb7re(,e)Fsgpii)sngauTdurbhitrcjieeeaactllt4eeleyadadv,sbbetiyos)nwaachreniirgtdoihhtwsrpteesaHm.sc(uia5pdl‐etaieertc)yadid‐eixncdeeisdteindgtuhieshRiOngS rain treatment. (c, hs)caTvheenlegaivnegs awbiitlhitpyHof4raicciedpralainnttsre, aetsmpeencti.a(ldly, iu) nTdheerlehaivgehs-wteimthppeHra3tuacreidconditions. rain treatment. (e, j) TheTloeaavlelsevwiaitthepoHxi2daactiidveradinamtreaagtme ternitg.gered by ambient stresses, plants have developed a series of physiological mechanisms for adaption [54]
Summary
The deleterious effects for crop production often originate from several ambient stresses occurring simultaneously [1]. Even though mild acid rain (pH 4.5~5.5) was reported to benefit seedling germination and shoot growth for certain plants [2], severe acid rain directly and indirectly influences the growth of crops by interfering with a considerable number of biochemical and physiological processes, altering several antioxidant enzyme-mediated reactions, accelerating lipid peroxidation, inhibiting photosynthesis and worsening the rhizosphere condition for nutrient uptake, which leads to nutrient disorder and morphological changes of plants [2,3,5,6,7]. Accompanying structural damages in the plasma membrane and chlorophyll, CO2 accumulates in intercellular space due to narrower stomata after exposure to acid rain whose pH was lower than pH 3, and the rate of photosynthesis is lowered [13]. The damaging effects induced by acid rain depend on pH value and nutrient condition
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