Chloroplast Auxin Efflux Mediated by ABCB28 and ABCB29 Fine-Tunes Salt and Drought Stress Responses in Arabidopsis.

Photosynthesis is among the first processes negatively affected by environmental cues and its performance directly determines plant cell fitness and ultimately crop yield. Primarily sites of photosynthesis, chloroplasts are unique sites also for the biosynthesis of precursors of the growth regulator auxin and for sensing environmental stress, but their role in intracellular auxin homeostasis, vital for plant growth and survival in changing environments, remains poorly understood. Here, we identified two ATP-binding cassette (ABC) subfamily B transporters, ABCB28 and ABCB29, which export auxin across the chloroplast envelope to the cytosol in a concerted action in vivo. Moreover, we provide evidence for an auxin biosynthesis pathway in Arabidopsis thaliana chloroplasts. The overexpression of ABCB28 and ABCB29 influenced stomatal regulation and resulted in significantly improved water use efficiency and survival rates during salt and drought stresses. Our results suggest that chloroplast auxin production and transport contribute to stomata regulation for conserving water upon salt stress. ABCB28 and ABCB29 integrate photosynthesis and auxin signals and as such hold great potential to improve the adaptation potential of crops to environmental cues.

Strigolactones affect phosphorus acquisition strategies in tomato plants.

Strigolactones (SLs) are plant hormones that modulate morphological, physiological and biochemical changes as part of the acclimation strategies to phosphorus (P) deficiency, but an in-depth description of their effects on tomato P-acquisition strategies under P shortage is missing. Therefore, in this study, we investigate how SLs impact on root exudation and P uptake, in qualitative and quantitative terms over time, in wild-type and SL-depleted tomato plants grown with or without P. Under P shortage, SL-depleted plants were unable to efficiently activate most mechanisms associated with the P starvation response (PSR), except for the up-regulation of P transporters and increased activity of P-solubilizing enzymes. The reduced SL biosynthesis had negative effects also under normal P provision, because plants over-activated high-affinity transporters and enzymatic activities (phytase, acidic phosphatase) to sustain elevated P uptake, at great carbon and nitrogen costs. A shift in the onset of PSR was also highlighted in these plants. We conclude that SLs are master kinetic regulators of the PSR in tomato and that their defective synthesis might lead both to suboptimal nutritional outcomes under P depletion and an unbalanced control of P uptake when P is available.

Implication of potassium on the quality of cherry tomato fruits after postharvest during cold storage.

The influence of the potassium (K) content in tomato fruits over compounds or antioxidant characteristics during the postharvest period in cold storage is little known. The aim of this work was to determine whether the effect of a biofortification programme with K in KCl form can improve the postharvest storage of cherry tomato fruits at 4 °C. K treatments applied during the crop cycle of the plants: 5, 10 and 15 mM of KCl. Biomass parameters, levels of K, antioxidant capacity test, Vitamin C, carotenoids, phenolic compounds and free polyamines in tomato cherry fruits were measured. Our results show that the treatment with 15 mM KCl prevents weight and water loss during postharvest storage at 4 °C, increases K concentration, and bolsters the antioxidant capacity, since the concentration in lycopenes as well as flavonoids and derivatives rose, while the contents in Vitamin C together with hydroxycinnamic acids and derivatives remained stable.

Effects of climatic control on tomato yield and nutritional quality in Mediterranean screenhouse.

BACKGROUND: The quality of vegetables for fresh consumption is a complex issue. In this study the yield and quality of cherry tomato fruits were assessed under different environmental control conditions, namely in a screenhouse (S), in a screenhouse equipped with a fogging system (SF) and in a screenhouse with complements such as plastic sheeting to maintain the microclimate created by the fogging system (SFS), as well as under open field (OF) cultivation. Levels of vitamin C, carotenoids (lycopene, ß-carotene and lutein), phenolic compounds (flavonoids and phenolic acids), sugars (fructose, glucose and sucrose), organic acids (citric acid and malic acid) and flavour indices were measured. The aim of the study was to determine how different environmental control technologies could influence production and quality traits in tomato cherry fruits cultivated in a Mediterranean area. RESULTS: The results showed that the fogging system treatment's decline in maximum vapour pressure deficit (by 0.7 kPa compared with OF cultivation), increase in mean fruit weight (by about 4 g per fruit) and low radiation and temperature values may exert a positive effect on lycopene accumulation. CONCLUSION: For the production and nutritional parameters measured, it is postulated that the fogging system treatment offers a better balance between production and nutritional quality. This treatment proved to be best in terms of productivity, vitamin C and lycopene contents and antioxidant capacity.