Presence of β-cyanoalanine synthase in unimbibed dry seeds and its activation by ethylene during pre-germination

Evolution of HCN from both rice ( Oryza sativa ) and cocklebur ( Xanthium pennsylvanicum ) seeds increased during a pre-germination period and preceded the evolution of (C₂H₄). These two species were adopted as the representatives of starchy and fatty seeds, respectively. Ethylene promotes seed germination of many species. However, HCN evolution declined abruptly when the radicles emerged and before the peak in C₂H₄ evolution. More-over, both rice and soybean ( Glycine max ) seeds showed some activity of β-cyanoalanine synthase (CAS, EC 4.4.1.9) even in the unimbibed dry state. The activities of CAS in the lower seed of cocklebur and in soybean seeds increased rapidly after emergence of the radicle. However, the CAS of rice seeds, with high activity in the dry state, exhibited a bimodal change, gradually decreasing until radicle emergence had occurred, but then increaing. It is thus likly that HCN evolution during initial imbibition may be derived from cyanogenic reserves and controlled by both pre-existing and subsequently-developing CAS. The exogenous application of C₂H₄ stimulated the activities of CAS in both rice and upper cocklebur seeds and reduced their cyanogen contents. Therefore, the decline of HCN evolution after germination seems to be due to the increased activities of CAS by endogenously produced C₂H₄.     

Iron toxicity and other chemical soil constraints to rice in highland swamps of Burundi

Iron toxicity is suspected to be a major nutritional disorder in rice cropping systems established on flooded organic soils that contain reductible iron. A pot trial was carried out to assess Fe toxicity to rice in flooded Burundi highland swamp soils with a wide range of organic carbon contents. Soil and leaf analyses were performed and total grain weight was determined. Clear Fe toxicity was diagnosed, based on leaf Fe content at panicle differentiation. Leaf Fe contents higher than 250 g g^–1 dry matter induced lower Mg (and probably Mn) uptake, and a 50% total grain weight reduction. These features were associated with exchangeable Fe equivalent fractions higher than 86%. Besides, several non-Fe toxic soils exhibited an Mg-Mn imbalance.     

水稻品种对白背飞虱种群增长的影响

白背飞虱在不同类型水稻品种上的分布、趋性、发育和繁殖力是不同的。它喜欢在杂交稻（汕优6号）上生活和繁殖,取食后成虫寿命最长,取食量、产卵趋性、产卵量、田间虫量均最大,种群增长快;在粳稻上却相反;常规灿稻和糯稻介于二者之间。在同一类型品种中,抗虫品种比感虫品种在上述特性方面差异明显。说明抗虫育种和种植抗虫品种是对该害虫综合治理的一项关键技术。     

棉铃虫对氰戊菊酯抗性和敏感品系的选育

用氰戊菊酯对来自阳谷的棉铃虫(YG)Heliothis armigera(Hubncr) 进行抗性晶系的筛选。在15代期间经过9代的室内选育,获得抗性品系(Fcn-R),抗性倍数高达2“3倍,筛选后F₁₅代LD₅₀值(24.1412μg/头)比筛选前F1代lD₅₀值(0.2020μg/头)提高了119.5倍。对来自偃师的棉铃虫(YS)进行了连续两代单对筛选,得到敏感品系(Fen-S),敏感晶系的LD50值为0.0116μg/头,接近1983年东台敏感晶系的LD₅₀值(0.0098μg/头)Fcn-R抗性晶系筛选前后分别测定了七种杀虫剂的剂量-死亡回归线,发现Fen-R抗性品系对溴氰菊酯[LD₅₀(Fen-R)/LD₅₀(YG)=5.2X] 和氯氰菊酯(2.5X)具有一定程度的交互抗性;而对功夫菊酯(0.66X),氯菊酯(0.89x)、灭多威(0.74X)及久效磷(1.5x)没有交互抗性。氰戊菊酯加Pb的增效试验结果表明棉铃虫对氰戊菊酯的抗性主要是由于多功能氧化酶的代谢作用。毒理学资料还暗示抗性为多因子(基因)的。     

Behavioral responses of the whitebacked planthopperSogatella furcifera (Homoptera: Delphacidae) on rice plants whose odors have been masked

In a two-choice test, moreS. furcifera females settled more often on exposed plants than on parafilm-masked ones, regardless of the susceptibility of rice varieties. This indicates that rice volatiles play an important role in the insect's short-range orientation to its host. The fact that more insects settled on exposed resistant Rathu Heenati (RHT) than to masked susceptible Taichung Native 1 (TN1) suggests that there must be certain common volatiles released by both varieties. Few females landed on masked plants of either RHT or TN1. This implies that the insect could not recognize at a distance that a plant was resistant or susceptible without olfactory stimuli.S. furcifera excreted less honeydew on masked plants than on exposed ones for both varieties and more on masked TN1 than on exposed RHT. The electronic monitoring of feeding behavior demonstrates that the insect made more frequent probes and had shorter phloem ingestion durations on exposed RHT than on exposed TN1 and on masked RHT than on masked TN1. Moreover, the insect had longer phloem ingestion durations on masked TN1 than on exposed RHT. These results suggest that volatile chemicals given off by resistant RHT plants have a negative effect on feeding.     

Ethylene production in rice bronzing leaves induced by ferrous iron

Bronzing, a nutritional disorder of rice plants which is widely distributed in tropical lowlands, was induced by dipping the cut end of rice leaves into FeSO₄ solution (pH 3.5). Ethylene production; the activities of peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase; and the effects of Co²⁺, aminoethoxyvinylglycine, Ag⁺, cycloheximide, and 1-aminocyclopropane-1-carboxylate, were investigated in the course of bronzing development. It was found that ethylene production could be stimulated up to about 20 times that of the control by Fe²⁺, and a peak could be reached at about 24 h after incubation. The Fe²⁺-treated leaves also had 10-fold higher peroxidase activity than the control, whereas in vitro enzyme activity was inhibited by Fe²⁺. Cycloheximide retarded in vivo stimulation of peroxidase, indicating that in vivo stimulation resulted from inducing de novo synthesis of the enzyme. No changes in the activities of phenylalanine ammonia-lyase and polyphenol oxidase were observed. The results, obtained from the incubation of leaves with Co²⁺, aminoethoxyvinylglycine, Ag⁺, cycloheximide, or 1-aminocyclopropane-1-carboxylate, showed that ethylene production was the effect of Fe²⁺ stress and that it was not involved in the process of bronzing development, which is probably an acclimation process to enable plants to cope with stress. The accelerated peroxidase activity may be associated with bronzing development.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - EFE ethylene forming enzyme - PAL phenylalanine ammonia-lyase - POD peroxidase - PPO polyphenol oxidase - SE standard error     

Glutelin accumulation and changes in the levels of its mRNA in the superior and inferior spikelets of rice ear during ripening

Glutelin accumulation in the apical spikelet of the top primary branch (superior spikelet) and the second spikelet of the lowest secondary branch (inferior spikelet) of the ear of the rice plant (Oryza sativa L.) was characterized during grain filling.In the superior spikelet, the accumulation of dry matter and nitrogen started immediately after flowering and rapidly reached the maturation level by 20 days after heading (DAH). At 7 DAH, total RNA content had already reached its maximum level and glutelin mRNA content 70% of its maximum. The increase in glutelin mRNA was followed by a rapid increase in glutelin between 7 and 16 DAH.In the inferior spikelet dry matter, nitrogen and glutelin accumulation were low immediately after flowering and increased only after grain filling of the superior spikelet was almost complete. Total RNA and glutelin mRNA increased much later at slower rates than in the superior spikelet.It is very likely that the retardation of dry matter, total nitrogen and glutelin accumulation in the inferior spikelet is due to retardation of differentiation and development of endosperm tissue, and to glutelin gene expression in endosperm cells. It is suggested that the delayed development resulted from limited partitioning of nutrients to the inferior spikelet at the early stage of ripening.