No abstract

No abstract

No abstract

Water stress is one of the most important abiotic factors affecting plants worldwide. This study compared the photochemical responses of two lineages of Crambe abyssinica (FMS CR 1307 and 1326) under water deficit (WD) conditions. The relative water content (RWC), stomatal conductance, chlorophyll (Chl) index, and Chl a fluorescence were evaluated. FMS CR 1326 showed greater reductions in RWC under WD. The FMS CR 1307 showed greater reductions in the connectivity of energy (L-band) and electron transfer from the oxygen-evolving complex (K-band), followed by a lower ability to maintain the reduction of plastoquinone. However, the increased size of the pool of the final electron acceptors in PSI for this lineage was observed. The FMS CR 1326 plant lineage showed an advantage over the FMS CR 1307 in terms of stability and efficiency of PSII under low water availability conditions.

During in vitro multiplication of horticulture plant species, synthetic cytokinins such as 6-benzylaminopurine (BA) can affect the microshoot formation. Murashige and Skoog culture medium (MS) can also act as a morphogenetic response modulator. The aim was to analyze the effects of BA and a gradient of MS salts on the morphophysiological status of Billbergia zebrina microshoots. Plantlets were cultured with a gradient of MS salts (50%, 100%, 150%, or 200%) supplemented with two BA levels (0 or 13 μM). After 50 days of culture, stomatal parameters, contents of photosynthetic pigments, and chlorophyll fluorescence were assessed. Plantlets cultured in all media without BA presented a low budding rate. In contrast, plantlets cultured with BA showed 100% budding. With 13 μM BA, the leaves presented bigger stomata and wider opening. Plantlets cultured with BA had lower contents of photosynthetic pigments. MS treatments without BA supplementation did not show any change in the pigments’ ratios. Plantlets cultured with BA had lower activity of the water-splitting complex and signs of photoinhibition damage. This resulted in the reduced performance of the photosynthetic apparatus. BA exposure can ensure the inducement of adventitious microshoots. BA at the tested concentration can induce morphophysiological disorders, irrespective of MS salt concentration.

at time t after start of actinic illumination; FV/F0 -ratio of the de-excitation rate constants for photochemical and nonphotochemical events; KP -photochemical de-excitation rate constant; PItotal -total performance index, which measures the performance up until the final electron acceptors of PSI; RC/CSm -total number of active reaction centers; SFI(ABS) -PSII structure and functioning index; VI -relative variable fluorescence at 30 ms (step I); VJ -relative variable fluorescence at 2 ms (step J); VK -relative variable fluorescence at 0.3 ms (step K); WK -represents the damage to oxygen-evolving complex; WL -indicates disturbance in the thylakoid membranes, reducing the energetic connectivity between the PSII units; ∆VIP -relative variable fluorescence amplitude of the increase from I to P = relative contribution of the increase from I to P to the increase in OJIP; φD0 -quantum yield of energy dissipation (at t = 0); φE0 -quantum yield of electron transport (at t = 0); φP0 -maximum quantum yield of primary photochemistry (at t = 0); φR0 -quantum yield of reduction of end electron acceptors at the PSI acceptor side; ψR0 -efficiency/probability by which electrons move from PSII to PSI acceptor side.

Determining drought tolerance in plants is an increasingly important feature due to the reduction of water resources, since water stress is one of the main environmental factors that limit agricultural growth and productivity. The objective of this study was to evaluate the tolerance of crambe (Crambe abyssinica Hochst) genotypes submitted to water stress induced by polyethylene glycol during germination and early growth of seedlings. A randomized block experimental design was used in a factorial scheme consisting of five crambe genotypes (FMS Brilhante, FMS CR 1203, 1307, 1312 and 1326) and five levels of osmotic potential [0.0 (control), -0.2, -0.4, -0.5 and -0.6 MPa] in five replicates of 40 seeds. Germination rate (%), normal seedling development (%), germination speed index, root and shoot length, total fresh matter, and water content of seedlings (%) were analyzed. Physiological quality of seeds and initial development of crambe genotypes was improved in the group submitted to Ψw = -0.2 MPa. Germination and vigor index of crambe seeds were hampered by reduction of the potential to -0.4 MPa. The genotype FMS CR 1203 was the most tolerant to water stress, whereas FMS CR 1307 and 1312 were the most sensitive, as corroborated by PCA.

Ft -fluorescence at time t after the beginning of actinic illumination; FV/F0 -ratio of the de-excitation rate constants for photochemical and nonphotochemical events; OEC -oxygen-evolving complex; PItotal -total performance index, which measures the performance up until the final electron acceptors of PSI; RC/CSm -total number of PSII active reaction centers; Sm/tFmax -average fraction of open RC in the period of 0 to tFmax (time of maximum fluorescence production); VI -relative variable fluorescence at 30 ms (step I); VJ -relative variable fluorescence at 2 ms (step J); VK -relative variable fluorescence at 0.3 ms (step K); WK -the damage to OEC; WL -indicates disturbance in the thylakoid membranes, reducing the energetic connectivity between the PSII units; δR0 -efficiency/probability with which an electron from the intersystem electron carriers moves to reduce end electron acceptors at the PSI acceptor side (RE); φD0quantum yield of energy dissipation (at t = 0); φE0 -quantum yield of electron transport (at t = 0); φP0 = FV/Fm -maximum quantum yield of primary photochemistry of PSII reaction center (at t = 0); φR0 -quantum yield of reduction of end electron acceptors at the PSI acceptor side (RE); ψR0 -efficiency/probability by which electrons move from PSII to the PSI acceptor side.