Exogenous Calcium Alleviates Nocturnal Chilling-Induced Feedback Inhibition of Photosynthesis by Improving Sink Demand in Peanut (Arachis hypogaea)

Arachis hypogaea (peanut) is a globally important oilseed crop with high nutritional value. However, upon exposure to overnight chilling stress, it shows poor growth and seedling necrosis in many cultivation areas worldwide. Calcium (Ca2+) enhances chilling resistance in various plant species. We undertook a pot experiment to investigate the effects of exogenous Ca2+ and a calmodulin (CaM) inhibitor on growth and photosynthetic characteristics of peanut exposed to low night temperature (LNT) stress following warm sunny days. The LNT stress reduced growth, leaf extension, biomass accumulation, gas exchange rates, and photosynthetic electron transport rates. Following LNT stress, we observed larger starch grains and a concomitant increase in nonstructural carbohydrates and hydrogen peroxide (H2O2) concentrations. The LNT stress further induced photoinhibition and caused structural damage to the chloroplast grana. Exogenous Ca2+ enhanced plant growth following LNT stress, possibly by allowing continued export of carbohydrates from leaves. Foliar Ca2+ likely alleviated the nocturnal chilling-dependent feedback limitation on photosynthesis in the daytime by increasing sink demand. The foliar Ca2+ pretreatment protected the photosystems from photoinhibition by facilitating cyclic electron flow (CEF) and decreasing the proton gradient (ΔpH) across thylakoid membranes during LNT stress. Foliar application of a CaM inhibitor increased the negative impact of LNT stress on photosynthetic processes, confirming that Ca2+–CaM played an important role in alleviating photosynthetic inhibition due to the overnight chilling-dependent feedback.

Differential Gene Expression Among Genotypes of the Genus Saccharum Contrasting in Biomass Production

The development of biomass crops aims to meet industrial yield demands to become a profitable and sustainable activity. Achieving these goals in an energy crop such as sugarcane relies on breeding for sucrose accumulation, fiber content and tillering capacity. Sucrose storage depends on transport from leaves to culms driven by enzymes involved in sucrose synthesis and hydrolysis. High biomass genotypes often use photosynthesis products to produce lignocellulosic compounds to form the cell wall. To expand the understanding of the pathways related to these traits, we evaluated gene expression of two groups of genotypes contrasting in biomass yield, as well as testing for differences among members within the same group. First visible dewlap leaves were collected from six genotypes of each group to perform RNA-Seq. We found evidence that both groups differ with regard to genomic stress caused by polyploidy, as indicated by the enrichment of genes involved in transposition activity and defense response processes. Although carbon assimilation terms were not enriched, genes annotated with such terms were co-expressed with those coding for members of hormonal pathways. Sucrose phosphate synthase and hydrolytic enzymes coding genes were upregulated in leaves of sucrose-accumulating genotypes, as genes coding for enzymes involved in the biosynthesis of lignin. Compared to other high biomass accessions, the hybrid US85-1008 presented upregulation of photosynthesis-related genes probably due to its sink demand to store sugar in culms. This study expands the knowledge of gene expression in sugarcane leaves, revealing differences between and within phenotypically distinct groups.

EFFECTS OF SHADE TREE SPATIAL DISTRIBUTION AND SPECIES ON PHOTOSYNTHETIC RATE OF COFFEE TREES

The use of shade trees in coffee fields have been motivated by climatic changes. However, microclimatic conditions in shaded coffee fields differ due to shade tree spatial distribution and species, altering physiological responses of coffee trees. This study aimed to evaluate the effects of shade tree spatial distribution and species on coffee trees photosynthetic rate in two growth seasons, of high (HSD) and low (LSD) sink demand. The experimental design consisted of randomized blocks with three replicates in split-split-plots. Plots were the shade tree species: <em>Anadenanthera falcata</em>, <em>Cassia grandis</em> and <em>Peltophorum dubium</em>. Split plot was formed by five distances between coffee trees and shade tree trunks: coffee trees on planting row of shade trees, distancing one (D1L) and five (D5L) meters from shade trees trunk; coffee trees on inter-rows of shade trees, parallel to D1L and D5L (D1E and D5E); coffee trees distancing 77 meters from shade tree trunks, in a full-sun field (PS). The split-split-plots correspond to coffee tree canopy exposure to the sun: branches facing North or South. Shade trees canopy density and occupation was evaluated with a convex densiometer. Photosynthetic rate (Pn)and photosynthetic active radiation (PAR) were measured with an Infrared Gas Analyzer (IRGA) on two time-frames, between 7.00 and 9.00 solar hours and between 11.00 and 13.00. Shade tree canopy density and occupation was not homogenous during the change of seasons and shift due to spatial distribution, which also changes PAR levels. Shade trees reduce PAR to more suitable values for coffee tree exploitation, especially on D1L and D5L. During HSD, shading did not affect P_n, which was greater in branches facing North. Yet, in LSD, between 11.00 and 13.00, coffee trees shaded with <em>A. falcata</em> showed greater P_n than at PS. Coffee trees shaded with <em>C. grandis</em> at D5L and D1E had greater values of P_n than PS.

Genotypic variation in pre- and post-anthesis dry matter remobilization in Iranian wheat cultivars: associations with stem characters and grain yield

The amount of carbohydrate accumulation and remobilization in the wheat stem can be estimated by monitoring changes in stem dry matter. Eighty-one wheat cultivars were examined in the Moghan region of Iran during the 2010–2011 and 2013–2014 growing seasons. Pre- and post-anthesis dry matter remobilization was quantified in the tested cultivars and their associations with stem characteristics and grain yield were investigated. There was substantial variation in stem length, weight, and specific weight among the tested cultivars. The majority of the cultivars did not show pre-anthesis dry matter remobilization in the stem or internodes. In contrast, most of them used stem dry matter that had been stored after anthesis, suggesting that under the given conditions, current photosynthesis along with post-anthesis dry matter remobilization could meet most of the sink demand. Generally, there were no significant associations between stem length and dry matter remobilization (r = –0.05 to 0.03; P ≥ 0.05). Stem weight (r = 0.42 to 0.65; P ≤ 0.01) and specific stem weight (r = 0.44 to 0.60; P ≤ 0.01) measured at 16 days after anthesis correlated positively and significantly with dry weight loss from the stem. Intriguingly, no clear relationships were found between dry matter remobilization and grain yield (r = –0.13 to 0.04; P ≥ 0.05), suggesting that there are no simple relationships between these traits. The association between dry matter remobilization and grain yield may be different depending on the examined cultivars.

Biochemical Profiling of Source and Sink Tissues at Different Growth Stages of Early and Late Maturing Varieties of Sugarcane (Saccharum spp. hybrids)

Sugarcane being C4 crop exhibits distinct source-sink signaling pathway that helps in storing remarkably high amount of sucrose in its sink tissues that makes it a highly remunerable crop worldwide. In the present study sugar content was profiled in both source and sink tissues of early (CoJ64) and late (BO91) maturing sugarcane varieties. At early growth stage (i.e. at 210 DAP) sink tissues of both varieties exhibited higher reducing sugar and low sucrose content while in source tissues both sucrose and reducing sugar content was observed high, depicted lower sink demand for sucrose. With maturity, when sink demand for sucrose storage increased, rise in sucrose content was seen in sink tissues, whereas in source tissues gradual decrease in sucrose and reducing sugar content was observed. Accumulation of sucrose was found much higher in CoJ64 than those in BO91. In CoJ64 maximum sucrose content (64.2%) was seen at 330 DAP while in BO91 it was 41.8% at 390 DAP. At this stage, source tissues too exhibited higher sucrose and reducing sugar content. Thus sucrose synthesis in source tissues and its transportation to the sink tissues is primarily governed by the sink demand.

Growth performance of castor bean hybrids under different plant densities

ABSTRACT Castor bean grown at high plant densities can increase yield due to increased light interception and reduction in sink demand. The objective of this study was to evaluate the effect of plant density on growth of castor bean hybrids. The experiment was conducted in Botucatu, SP, Brazil, in a split plot randomized block design, with four replications, in 2011 and 2012. The main plot consisted of the sampling times and the subplots consisted of a 3x3 factorial, with the 3 genotypes in the first factor and the 3 plant densities in the second factor. The variables analyzed were: dry mass of leaves, stems, racemes, and total dry matter, which were measured at 30, 60, 90, 120 and 150 days after emergence (DAE). Data were examined for significant differences using analysis of variance followed by the F test (p < 0.05). When interaction was found between the factors and sampling the means were analyzed by regression analysis (p < 0.05). Growth performance was higher in 2012 because of the greater water availability. In 2011, under lower rainfall, there was less branching resulting in cycle end, with total leaf loss. High plant densities partially suppress the development of higher-order structures, especially when associated with water restriction.