| Abrupt drought-flood alternation is characterized by persistent drought during the early stage of the rice growth followed by the rapid transition from drought to flooding due to a heavy continuous rain.It is a kind of meteorological disasters that frequently occur in the south of China around the Yangtze River basin,causing a severe reduction of crop yield in lots of areas,even the complete loss.Located in the southern part of the middle reaches of the Yangtze River,Jiangxi is an important double cropping rice production area in China where drought and flood disasters occur frequently,especially the abrupt drought-flood alternation disasters,which brings seriously damage to the rice production.At present,study on the rice yield formation and related physiological characteristics at panicle differentiation stage under abrupt drought-flood alternation is not deep enough.Therefore,it is particularly important to carry out research on the yield formation mechanism under abrupt drought-flood alternation at panicle differentiation stage and the yield recovery after abrupt drought-flood alternation.In this study,the disaster-causing characteristics of abrupt drought-flood alternation at panicle differentiation stage of double cropping rice and the yield recovery effects of different exogenous substances were discussed,mainly including:(1)The double cropping early and late rice varieties were selected as the materials,according to the period of abrupt drought-flood alternation in this area.The double cropping early and late rice varieties were treated by different water treatments of no drought and no flood(CK0),drought without flood(CK1),no drought with flood(CK2),abrupt drought-flood alteration(T1)during the young panicle differentiation initiation stage,and the physiological and biochemical indexes such as photosynthetic,antioxidant enzymes,osmotic regulation and so on were determined.In addition,proteomics and metabonomics were used to analyze the disaster response mechanism of double cropping early rice under abrupt drought-flood alternation at the panicle differentiation stage.(2)More than ten kinds of recovery measures including nitrogen(N)supply after abrupt drought-flood alternation(T1?N)were set up,and the physiological basis and transcriptional translation mechanism were studied.The main findings are as follows:1.The yield per plant of double cropping early and late rice was decreased in different degrees under drought,flood and abrupt drought-flood alternation treatment.Compared with CK0,the yield per plant of early rice CK1,CK2,T1 were decreased by55.79,38.02,63.40%,and the late rice was decreased by 57.78,37.31,61.07%,respectively.Both the early and late rice declined the most with T1.In general,the effect of drought on rice yield formation was greater than that of flood.The net photosynthetic rate of early and late rice leaves decreased at different degree at the early stage of drought,flood and abrupt drought-flood alternation,among which the net photosynthetic rate of CK1 and T1 decreased greatly.The SOD,POD and CAT enzyme activity in early and late rice leaves was significantly higher than that of CK0,and MDA content also increased to different degrees.The soluble protein and soluble sugar content of T1 were significantly decreased.2.In this study,the rice spike metabolites of were identified by LC-MS(liquid chromatograph-mass spectrometry),and quantitative analysis of spike total protein was conducted by i TRAQ(isobaric tags for relative and absolute quantification).The 522 differentially expressed proteins(DEPs)and 107 differential metabolites(DMs)were identified from rice spike between T1 and CK0 treatment.528 DEPs and 110 DMs were identified from rice spike between T1 and CK1 treatment.82 DEPs and 124 DMs were identified from rice spike between T1 and CK2 treatment.The DMs and DEPs indicated that photosynthesis metabolism,energy metabolism pathway and reactive oxygen species response have changed greatly under abrupt drought-flood alteration stress,which are the important reasons for the rice yield reduction.3.More than ten different exogenous growth regulators including N were applied to study the recovery effects.The results showed that the yield of N supply after abrupt drought-flood alternation stress had an outstanding recovery effects on both double cropping early and late rice.The main reason lies in the increase of effective panicle number per plant.The application of N led to the regulation of physiological and biochemical processes which including the balance of endogenous hormones,the activity of N metabolism-related enzymes,the activity of antioxidant enzymes,photosynthesis,the accumulation of osmotic adjustment substances,the accumulation and transport of dry matter,and the absorption and use of N,which led to a rapid growth recovery effect after abrupt drought-flood alternation stress in rice.4.Using ribosome profiling combined with RNA sequencing(RNA-seq)technology,the interactions between transcription and translation during N-induced recovery after abrupt drought-flood alternation were analyzed.The result showed that a small proportion of response genes(14.0% of genes whose expression was upregulated and 6.6% of genes whose expression was downregulated)were shared at the transcription level and translation level.Further analysis revealed that the translation efficiency(TE)of the genes was influenced by their sequence characteristics,including their GC content,coding sequence length and normalized minimal free energy.Genome-wide analysis found that 7003 genes contained upstream open reading frames(u ORFs).Compared with the number of untranslated u ORFs,the increased number of translated u ORFs promoted the improvement of TE.The TE of the u ORFs of N application after abrupt drought-flood alteration was lower than that of the u ORFs of abrupt drought-flood alternation on a genome-wide basis.This study characterizes the genome-wide translational regulatory pattern in response to N supplied after abrupt drought-flood alternation stress.In this study,it was found that drought,flood and abrupt drought-flood alternation were unfavorable to yield of double cropping early and late rice during the young panicle differentiation stage,especially the abrupt drought-flood alternation brought serious damage to the rice yield,indicating that abrupt drought-flood alternation stress created a synergistic effect to the reduction of yield.This study also explored the yield recovery effect of different exogenous substances after abrupt drought-flood alternation,in which the recovery of N supply is better.and this study defined the genome-wide translational regulatory pattern in response to N supplied after abrupt drought-flood alternation stress,which is helpful to understand the highly dynamic translation mechanism of rice and provides insights for future field production and breeding. |
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