THE CYANOBACTERIAL CHLOROPHYLL‐BINDING‐PROTEIN ISIA ACTS TO INCREASE THE IN VIVO EFFECTIVE ABSORPTION CROSS‐SECTION OF PSI UNDER IRON LIMITATION1

Iron availability limits primary production in >30% of the world’s oceans; hence phytoplankton have developed acclimation strategies. In particular, cyanobacteria express IsiA (iron‐stress‐induced) under iron stress, which can become the most abundant chl‐binding protein in the cell. Within iron‐limited oceanic regions with significant cyanobacterial biomass, IsiA may represent a significant fraction of the total chl. We spectroscopically measured the effective cross‐section of the photosynthetic reaction center PSI (σ_PSI) in vivo and biochemically quantified the absolute abundance of PSI, PSII, and IsiA in the model cyanobacterium Synechocystis sp. PCC 6803. We demonstrate that accumulation of IsiA results in a ～60% increase in σ_PSI, in agreement with the theoretical increase in cross‐section based on the structure of the biochemically isolated IsiA‐PSI supercomplex from cyanobacteria. Deriving a chl budget, we suggest that IsiA plays a primary role as a light‐harvesting antenna for PSI. On progressive iron‐stress in culture, IsiA continues to accumulate without a concomitant increase in σ_PSI, suggesting that there may be a secondary role for IsiA. In natural populations, the potential physiological significance of the uncoupled pool of IsiA remains to be established. However, the functional role as a PSI antenna suggests that a large fraction of IsiA‐bound chl is directly involved in photosynthetic electron transport.     

Gas Exchange and Flowering in Verticillium-wilted Pepper Plants

In Navarra, Northern Spain, Verticillium dahliae Kleb. is one of the pathogens that causes drastic reductions in pepper production. The aim of this study therefore was to describe how infection by V. dahliae affects gas exchange during the flowering of pepper in order to determine some possible factors contributing to the significant decrease of plant yield. Verticillium was inoculated when plants had started flowering. The first leaf wilting symptoms appeared on day 18 after inoculation, but leaf water potential rapidly decreased after infection. The inoculated plants produced more flowers than the controls between 15 and 33 days after inoculation, but flower production declined after day 33. Inoculated plants also suffered more defoliation and chlorophyll degradation. Leaf conductance and photosynthesis clearly decreased in both groups of plants as a consequence of senescence, but the values in those inoculated were significantly lower. Results suggest that the decrease in photosynthesis was in part due to defoliation and chlorophyll degradation, as well as premature flower fall. These factors contributed to the negative effects of Verticillium infection on pepper yield.     

The effect of leaffolder Cnaphalocrocis medinalis (Guenee) [Lepidoptera: Pyralidae] injury on the plant physiology and yield loss in rice

Influence of leaffolder feeding on chlorophyll, PS II activity and plant–water relations, effect of larval density on leaf damage and time course studies on larval feeding behaviour on altered physiological changes in TN1 rice culture were studied. Quantification of yield losses in the field caused by leaffolder was also assessed. Leaffolder damage resulted in 57% reduction in chlorophyll content, 23% reduction in PS II activity and 23% reduction in relative water content in comparison with control. Rice leaffolder larva folds the leaf and scrapes the green tissue from within the fold resulting in scorching and drying of the leaves. Larval density had differentially influenced effective leaf area of rice crop. Larval densities of more than 3 larvae per hill at maximum tillering stage resulted up to 20% unfilled grains, 28–57% reduction in PS II activity and 23% reduction in relative water content in comparison with the control. At flowering stage, flag leaf area damage of above 25% resulted in more than 50% unfilled grains over control, indicating direct effect of yield reduction in rice. Thus, a cumulative effect of loss in chlorophyll, reduced photosynthate availability and altered water relations caused by the leaffolder injury to flag leaf lead to greater yield loss in rice.     

Fluctuating sex ratios,but no sex-biased dispersal,in a promiscuous fish

Dispersal in birds and mammals tends to be female-biased in monogamous species and male-biased in polygamous species. However results for other taxa, most notably fish, are equivocal. We employed molecular markers and physical tags to test the hypothesis that Atlantic salmon, a promiscuous species with intense male-male competition for access to females, displays male-biased dispersal. We found significant variation in sex ratios and in asymmetric gene flow between neighbouring salmon populations, but little or no evidence for sex-biased dispersal. We show that conditions favouring male dispersal will often be offset by those favouring female dispersal, and that spatial and temporal variation in sex ratios within a metapopulation may favour the dispersal of different sexes in source and sink habitats. Thus, our results reconcile previous discrepancies on salmonid dispersal and highlight the need to consider metapopulation dynamics and sex ratios in the study of natal dispersal of highly fecund species.     

Activity of the System for Chlorophyll Biosynthesis and Structural and Functional Organization of Chloroplasts in a Plastome <Emphasis Type="Italic">en:chlorina-5</Emphasis> Sunflower Mutant

Chlorophyll (Chl) deficiency in leaves of a plastome sunflower (Helianthus annuus L.) en:chlorina-5 mutant is due to the formation of smaller chloroplasts with a markedly reduced membrane system, as compared to the parent 3629 line. Abnormalities in the structure of the photosynthetic apparatus in the mutant can be mainly attributed to changes in the formation of photosystem I and its light-harvesting complexes. Chl deficiency in en:chlorina-5 correlated with its lower capability of synthesizing the first specific Chl precursor, 5-aminolevulinic acid (ALA) in the light. Light-independent stages of Chl biosynthesis in the mutant had the same efficiency as in leaves of the parent line. ALA formation in darkness and its conversion into protochlorophyllide did not depend on the extent of photosynthetic membrane development and photosynthetic activity.     

缺铁使大豆叶片激发能的耗散增加

缺铁叶片的光合速率大幅度下降。这种降低可能不是色素含量降低的结果 ;而且缺铁对PSII复合物的活性影响很小 ;较高的PQ还原程度显示缺铁叶片PSII受体侧电子传递受阻 ,这可能是导致光合速率下降的主要因素。强光下缺铁叶片的天线转化效率比正常叶片低 ,用于光化学反应的激发能很少。缺铁导致大豆叶片激发能耗散增加。通过抑制剂处理和叶黄素组分的分析 ,可以认为在耗散过剩激发能的过程中 ,缺铁叶片充分启动了叶黄素循环     

Factor Affecting Sex Ratios of a Mermithid Parasite of Mosquitoes

The ratio of male to female Reesimermis nielseni Tsai and Grundmann, a nematode parasite of mosquito larvae, increased as the number of parasites per host increased. Hosts with a single nematode produced 9% males compared with essentially 100% males in hosts with more than 7 parasites; hosts with 3 nematodes produced about equal numbers of males and females. Males of R. nielseni generally emerged before females because of the earlier death of multiple-infected mosquitoes. The species of the host mosquito influenced the sex ratio, but the size of a specific host at the time of invasion did not. Host diet also had a noticeable influence on the sex ratio of the nematode: singly infected hosts from a starved population produced 92% males compared with 13% in the normally fed group. The importance of these factors in the mass rearing of R. nielseni is discussed.     

应用非光化学淬灭初始变化率作为浮游植物光保护能力指标的可行性

在非光化学淬灭(Non-Photochemical Quenching,NPQ)荧光诱导的早期(1 min),NPQ随时间的变化率(NPQ/t)可作为衡量浮游植物光保护能力的指标,与常用的传统指标NPQm(最大NPQ)相比,这一新指标具有更易标准化、测量效率更高且包含的信息更丰富的优点。通过实验测量和理论推导证明了NPQ/t的常数性质,并通过可控光照条件下的室内培养实验证明了应用NPQ/t反映浮游植物光保护能力的合理性和有效性:NPQ/t和NPQm、光保护色素浓度呈线性相关,高光强下培养的藻类其NPQ/t高于低光强下培养的藻类,不同藻种之间的NPQ/t:扁藻(Tetraselmis chui)牟氏角毛藻(Chaetoceros mulleri)叉鞭金藻(Dicrateria inornata)。这一方法解决了野外实测研究中传统指标难以满足结果标准化和快速测量等要求的问题,对于推动浮游植物光保护生态学研究具有重要意义。     

低温光照下与黄瓜子叶叶绿素降低有关的酶促反应

黄瓜子叶在低温光照下处理时,随着时间的延长,Chl含量和CAT活性显著下降,POD和AsA-POD在开始24h活性亦有下降趋势,随后POD活性显著增加,而AsA-POD活性仅稍有提高。Chl含量的减少和CAT活性降低之间呈正相关,与POD活性的增加呈负相关。低温、光照处理的黄瓜子叶内Chl的降低可被亚胺环己酮(CHM)延缓,被AsA、Vit E、没食子酸丙酯(PG)和DCMU抑制,但被H_2O_2,乙醇酸钠和甲基紫精(MV)加速。     

驳枝对早花烟草成熟期间叶中叶绿素含量、硝酸还原酶和淀粉酶活性的影响

对早花烟草驳枝后,其成熟期间中部和上部叶中叶绿素（Ch1）含量和硝酸还原酶（NR）活性下降,下部叶则增高,成熟后期的上部叶中淀粉酶（AM）活性明显增强。经驳枝的烟草,中、上部叶烘烤后叶中淀粉、氮和烟碱含量下降,下部叶中的淀粉含量无明显变化。