Zinc deficiency affects physiological and anatomical characteristics in maize leaves.

Zinc (Zn) is an essential microelement involved in several plant physiological processes. Therefore, it is important to identify Zn deficiencies promptly--before extensive damage occurs to the plant. The diagnostic tools that are used to identify Zn deficiencies are very important in areas where Zn deficiencies occur. Such diagnostic tools are vital for nutritional management and fertilizer recommendations. The current study investigated the effects of Zn deficiency on maize plants by recording a number of physiological and anatomical parameters. A Zn omission trial (from 0 to 22 days) was carried out to produce plants that had varying degrees of Zn deficiency. Typical symptoms of Zn deficiency (e.g. chlorotic stripes and purple shades on the edges and leaf sheath) appeared 16 days after the omission of Zn from nutrient solutions. As the time of Zn omission increased, there were significant decreases in net photosynthesis, stomatal conductance, maximal efficiency of photosystem I (evaluated by Fv/Fm), biomass (dry weight) and Zn concentrations in plants. Zinc-deficient plants also had a lower vascular bundle proportion coupled with a higher stomata density. These physiological and anatomical changes negatively impacted plant growth. Moreover, they occurred before visible symptoms of Zn deficiency were observed. Zinc concentrations were recorded for younger leaves, rather than for more mature leaves, which is usually recommended for plant analysis. The results demonstrate that the analysis of Zn in young leaves of maize is a very sensitive indicator of Zn status.

Understanding the low photosynthetic rates of sun and shade coffee leaves: bridging the gap on the relative roles of hydraulic, diffusive and biochemical constraints to photosynthesis.

It has long been held that the low photosynthetic rates (A) of coffee leaves are largely associated with diffusive constraints to photosynthesis. However, the relative limitations of the stomata and mesophyll to the overall diffusional constraints to photosynthesis, as well as the coordination of leaf hydraulics with photosynthetic limitations, remain to be fully elucidated in coffee. Whether the low actual A under ambient CO2 concentrations is associated with the kinetic properties of Rubisco and high (photo)respiration rates also remains elusive. Here, we provide a holistic analysis to understand the causes associated with low A by measuring a variety of key anatomical/hydraulic and photosynthetic traits in sun- and shade-grown coffee plants. We demonstrate that leaf hydraulic architecture imposes a major constraint on the maximisation of the photosynthetic gas exchange of coffee leaves. Regardless of the light treatments, A was mainly limited by stomatal factors followed by similar limitations associated with the mesophyll and biochemical constraints. No evidence of an inefficient Rubisco was found; rather, we propose that coffee Rubisco is well tuned for operating at low chloroplastic CO2 concentrations. Finally, we contend that large diffusive resistance should lead to large CO2 drawdown from the intercellular airspaces to the sites of carboxylation, thus favouring the occurrence of relatively high photorespiration rates, which ultimately leads to further limitations to A.

Development of the banana plants 'Prata Anã' and 'FHIA-01' under the effect of paclobutrazol applied on the soil.

Under some cultivation conditions, excessive growth of the pseudostem of banana plants can be considered a limiting factor, and thus, the use of growth regulators can constitute a valid alternative. This work aimed to evaluate the action of paclobutrazol on the growth of the pseudostem of banana plants and other characteristics of their development. An experiment was installed with five paclobutrazol doses (0; 0.5; 1.0; 1.5; and 2.0 g of a.i. plant-1) combined with two banana plant cultivars ('Prata Anã' and 'FHIA-01'). Paclobutrazol did not affect the number of days from planting to flowering, total leaf area and leaf emission rate. However, it increased leaf permanence on the plants and sucker number, reduced the foliar area of the leaves emitted after its application and provided an average reduction in pseudostem height of 26%.

Development of the banana plants 'Prata Anã' and 'FHIA-01' under the effect of paclobutrazol applied on the soil

Under some cultivation conditions, excessive growth of the pseudostem of banana plants can be considered a limiting factor, and thus, the use of growth regulators can constitute a valid alternative. This work aimed to evaluate the action of paclobutrazol on the growth of the pseudostem of banana plants and other characteristics of their development. An experiment was installed with five paclobutrazol doses (0; 0.5; 1.0; 1.5; and 2.0 g of a.i. plant-1) combined with two banana plant cultivars ('Prata Anã' and 'FHIA-01'). Paclobutrazol did not affect the number of days from planting to flowering, total leaf area and leaf emission rate. However, it increased leaf permanence on the plants and sucker number, reduced the foliar area of the leaves emitted after its application and provided an average reduction in pseudostem height of 26 percent.

Em algumas condições de cultivo o crescimento excessivo do pseudocaule de bananeiras pode ser considerado um fator limitante, assim a utilização de reguladores de crescimento pode constituir uma alternativa. O presente trabalho teve por objetivo avaliar a ação do paclobutrazol sobre o crescimento do pseudocaule de bananeiras e outras características do seu desenvolvimento. Para isso foi instalado um experimento com cinco doses do paclobutrazol (0; 0,5; 1,0; 1,5; e 2,0 g de i.a.planta-1) combinadas com dois cultivares de bananeira ('Prata Anã' e 'FHIA-01'). O paclobutrazol não afetou o número dedias do plantio ao florescimento, a área foliar total e a taxade emissão de folhas. Contudo, aumentou a permanência das folhas nas plantas e o número de perfilhos, reduziu a área foliar das folhas emitidas após a sua aplicação e proporcionou uma redução média de 26 por cento na altura do pseudocaule.

Synergism and negative interference during co-infection of tomato and Nicotiana benthamiana with two bipartite begomoviruses.

In Brazil, at least eight begomoviruses including Tomato rugose mosaic virus (ToRMV) and Tomato yellow spot virus (ToYSV) infect tomatoes. ToYSV symptoms in tomato and Nicotiana benthamiana appear earlier and are more severe compared to those of ToRMV. We investigated the role of several factors in this differential adaptation. To analyze infection kinetics, a single leaf was inoculated and subsequently detached after different periods of time. Viral DNA accumulation was quantified in plants, viral replication was analyzed in protoplasts, and tissue tropism was determined by in situ hybridization. Results indicate that ToYSV establishes a systemic infection and reaches a higher concentration earlier than ToRMV in both hosts. ToRMV negatively interferes with ToYSV during the initial stages of infection, but once systemic infection is established this interference ceases. In N. benthamiana, ToYSV invades the mesophyll, while ToRMV is phloem-restricted. During dual infection in this host, ToYSV releases ToRMV from the phloem.