The alternative oxidase in roots of Poa species

The main function of respiration is the production of energy-rich molecules (ATP). A major part (up to 60%) of the respiration in plants can occur via the nonphosphorylating alternative pathway, even under conditions when the sugar concentration is low. This suggests that the energetically 'wasteful' alternative pathway has a crucial function in plant metabolism. This alternative pathway does not produce energy in the form of ATP. The proposed function of the alternative pathway is the prevention of the production of excessive amounts of oxygen free radicals. The alternative pathway consists of only one protein, the alternative oxidase (AOX). This protein has been studied in detail in isolated mitochondria and several regulatory mechanisms have been discovered (pyruvate, reduction state of the protein, substrate concentration). This thesis analyses the role of these putative regulatory mechanisms in modifying the altrenative oxidase activity in intact roots of a range of grasses

Continuous Light as a way to increase Greenhouse Tomato Production

Tomato plants need six hours of darkness per day for optimal growth; therefore, photosynthesis does not take place for 25% of the day. If tomatoes could be grown under continuous light, a substantial increase in production is expected. In practice, however, continuous light-grown tomato plants develop a potentially lethal mottled chlorosis. Such continuous-light-induced injury is only poorly understood so far. Recently, we proposed a number of hypotheses that aim to explain the continuous-light-induced injury, and rediscovered that wild-tomato species were reported as continuous-light-tolerant. Here, we (i) present a simulation study which shows that if an ideal continuous-light-tolerant tomato genotype is used and no crop adaptations to continuous light are assumed, greenhouse tomato production could be 26% higher when using supplementary lighting for 24 h day-1 in comparison with using supplementary lighting only for 18 h day-1 during day time, and (ii) discuss expected changes in greenhouse energy budgets and alterations in crop physiological responses that might arise from cultivating tomatoes under continuous light

Regulation of Alternative Oxidase Activity in Six Wild Monocotyledonous Species. An in Vivo Study at the Whole Root Level1

The activity of the alternative pathway is affected by a number of factors, including the level and reduction state of the alternative oxidase (AOX) protein, and the reduction state of the ubiquinone pool. To investigate the significance of these factors for the rate of alternative respiration in vivo, we studied root respiration of six wild monocotyledonous grass species that were grown under identical controlled conditions. The activity of the alternative pathway was determined using the oxygen isotope fractionation technique. In all species, the AOX protein was invariably in its reduced (high activity) state. There was no correlation between AOX activity and AOX protein concentration, ubiquinone (total, reduced, or oxidized) concentration, or the reduction state of the ubiquinone pool. However, when some of these factors are combined in a linear regression model, a good fit to AOX activity is obtained. The function of the AOX is still not fully understood. It is interesting that we found a positive correlation between the activity of the alternative pathway and relative growth rate; a possible explanation for this correlation is discussed. Inhibition of the AOX (with salicylhydroxamic acid) decreases respiration rates less than the activity present before inhibition (i.e. measured with the 18O-fractionation technique)

Continuous-light tolerance in tomato is graft-transferable

Continuous light induces a potentially lethal injury in domesticated tomato (Solanum lycopersicum) plants. Recently, continuous-light tolerance was reported in several wild tomato species, yet the molecular mechanisms underpinning tolerance/sensitivity are still elusive. Here, we investigated from which part of the plant continuous-light tolerance originates and whether this trait acts systemically within the plant. By exposing grafted plants bearing both tolerant and sensitive shoots, the trait was functionally located in the shoot rather than the roots. Additionally, an increase in continuous-light tolerance was observed in sensitive plants when a continuous-light-tolerant shoot was grafted on it. Cultivation of greenhouse tomatoes under continuous light promises high yield increases. Our results show that to pursuit this, the trait should be bred into scion rather than rootstock lines. In addition, identifying the nature of the signal/molecule(s) and/or the mechanism of graft-induced, continuous-light tolerance can potentially result in a better understanding of important physiological processes like long-distance signaling

Plants under continuous light

Continuous light is an essential tool for understanding the plant circadian clock. Additionally, continuous light might increase greenhouse food production. However, using continuous light in research and practice has its challenges. For instance, most of the circadian clock-oriented experiments were performed under continuous light; consequently, interactions between the circadian clock and the light signaling pathway were overlooked. Furthermore, in some plant species continuous light induces severe injury, which is only poorly understood so far. In this review paper, we aim to combine the current knowledge with a modern conceptual framework. Modern genomic tools and rediscovered continuous light-tolerant tomato species (Solanum spp.) could boost the understanding of the physiology of plants under continuous ligh

A single locus confers tolerance to continuous light and allows substantial yield increase in tomato

An important constraint for plant biomass production is the natural day length. Artificial light allows for longer photoperiods, but tomato plants develop a detrimental leaf injury when grown under continuous light—a still poorly understood phenomenon discovered in the 1920s. Here, we report a dominant locus on chromosome 7 of wild tomato species that confers continuous light tolerance. Genetic evidence, RNAseq data, silencing experiments and sequence analysis all point to the type III light harvesting ¿chlorophyll a/b binding protein 13 (¿CAB-13) gene as a major factor responsible for the tolerance. In Arabidopsis thaliana, this protein is thought to have a regulatory role balancing light harvesting by photosystems I and II. Introgressing the tolerance into modern tomato hybrid lines, results in up to 20% yield increase, showing that limitations for crop productivity, caused by the adaptation of plants to the terrestrial 24-h day/night cycle, can be overcome

Kinome profiling reveals an interaction between jasmonate, salicylate and lifht control of hyponastic petiole growth in Arabidopsis thaliana

Plants defend themselves against infection by biotic attackers by producing distinct phytohormones. Especially jasmonic acid (JA) and salicylic acid (SA) are well known defense-inducing hormones. Here, the effects of MeJA and SA on the Arabidopsis thaliana kinome were monitored using PepChip arrays containing kinase substrate peptides to analyze posttranslational interactions in MeJA and SA signaling pathways and to test if kinome profiling can provide leads to predict posttranslational events in plant signaling. MeJA and SA mediate differential phosphorylation of substrates for many kinase families. Also some plant specific substrates were differentially phosphorylated, including peptides derived from Phytochrome A, and Photosystem II D protein. This indicates that MeJA and SA mediate cross-talk between defense signaling and light responses. We tested the predicted effects of MeJA and SA using light-mediated upward leaf movement (differential petiole growth also called hyponastic growth). We found that MeJA, infestation by the JA-inducing insect herbivore Pieris rapae, and SA suppressed low light-induced hyponastic growth. MeJA and SA acted in a synergistic fashion via two (partially) divergent signaling routes. This work demonstrates that kinome profiling using PepChip arrays can be a valuable complementary ∼omics tool to give directions towards predicting behavior of organisms after a given stimulus and can be used to obtain leads for physiological relevant phenomena in planta