Foliar cytokinins or brassinosteroids applications influence the rice plant acclimatization to combined heat stress.

The effect of different foliar sprays numbers of cytokinins - (CK) and brassinosteroids - (BR) on the physiological, biochemical, and panicle parameters of rice plants subjected to combined heat stress (high day/night temperatures) were studied in three different experiments. The treatments established for the first (E1) and second (E2) experiments were the following: i) absolute control, ii) stress control, iii) heat stress + one foliar spray of CK, iv) heat stress + two foliar sprays of CK, v) heat stress + three foliar sprays of CK, vi) heat stress + one foliar spray of BR, vii) heat stress + two foliar sprays of BR, or viii) heat stress + three foliar sprays of BR. For the third experiment (E3), the treatments were the following: i) absolute control, ii) stress control, iii) heat stress + three foliar applications of CK, iv) heat stress + three foliar applications of BR. Rice-stressed plants and sprayed with three foliar sprays of CK or BR had a better stomatal conductance in E1 and E2 compared to their heat-stressed control. The relative tolerance index suggests that three CK or BR applications helped to mitigate the combined heat stress in both experiments. The foliar CK or BR applications at the flowering and grain-filling stages in rice-stressed plants increased Fv/Fm ratio and panicle characteristics (number of filled spikelets and the percentage of panicle blanking in E3). In conclusion, foliar applications of BR or CK can be considered an agronomic strategy to help improve the negative effect of combined heat stress conditions on the physiological behavior of rice plants during different phenological stages.

Foliar Growth Regulator Sprays Induced Tolerance to Combined Heat Stress by Enhancing Physiological and Biochemical Responses in Rice.

Rice yield has decreased due to climate variability and change in Colombia. Plant growth regulators have been used as a strategy to mitigate heat stress in different crops. Therefore, this study aimed to evaluate the effect of foliar applications of four growth regulators [auxins (AUX), brassinosteroids (BR), cytokinins (CK), or gibberellins (GA)] on physiological (stomatal conductance, total chlorophyll content, Fv/Fm ratio, plant canopy temperature, and relative water content) and biochemical (Malondialdehyde (MDA) and proline contents) variables in two commercial rice genotypes exposed to combined heat stress (high day and nighttime temperatures). Two separate experiments were carried out using plants of two rice genotypes, Fedearroz 67 ("F67") and Fedearroz 2000 ("F2000") for the first and second experiments, respectively. Both trials were analyzed together as a series of experiments. The established treatments were as follows: absolute control (AC) (rice plants grown under optimal temperatures (30/25°C day/nighttime temperatures), heat stress control (SC) [rice plants only exposed to combined heat stress (40/30°C)], and stressed rice plants and sprayed twice (5 days before and after heat stress) with a plant growth regulator (stress+AUX, stress+BR, stress+CK, or stress+GA). The results showed that foliar CK sprays enhanced the total chlorophyll content in both cultivars (3.25 and 3.65 mg g-1 fresh weight for "F67" and "F2000" rice plants, respectively) compared to SC plants (2.36 and 2.56 mg g-1 fresh weight for "F67," and "F2000" rice plants, respectively). Foliar CK application also improved stomatal conductance mainly in "F2000" rice plants compared to their heat stress control (499.25 vs.150.60 mmol m-2s-1). Foliar BR or CK sprays reduced plant canopy temperature between 2 and 3°C and MDA content in plants under heat stress. The relative tolerance index suggested that foliar CK (97.69%), and BR (60.73%) applications helped to mitigate combined heat stress mainly in "F2000" rice plants. In conclusion, foliar BR or CK applications can be considered an agronomic strategy to help to ameliorate the negative effect of combined heat stress conditions on the physiological behavior of rice plants.

In vitro culture from mature seeds of Passiflora species

The genus Passiflora comprises hundred species, mainly native of the South American tropics and rainforests, which are grouped into 21 subgenera. Some species are widely studied for their economic importance and are chiefly cultivated for production of fruit juice. To obtain a continuous source of material for a screening of secondary metabolites, zygotic embryo culture was attempted for 62 Passiflora species, starting from seeds mainly collected in the wild. Twenty nine of these species produced calli, which had very different growth rates. Plants were successfully regenerated from calli of 13 different species. For 25 of the responsive species this is the first report of in vitro culture.

O gênero Passiflora compõe centenas de espécies, a maioria de origem dos trópicos e das florestas da América do Sul, as quais são agrupadas em 21 subgêneros. Algumas espécies foram intensamente estudadas por sua importância econômica e são cultivadas principalmente para a produção de suco de fruta. Cultura de 29 espécies de Passiflora foram obtidos a partir de embriões zigóticos e de culturas de endosperma. Foram obtidos diferentes tipos de calos de crescimento, de tal forma que plantas foram regeneradas a partir de calos de 13 espécies diferentes. Não haviam sido ainda relatadas culturas in vitro para 25 das espécies trabalhadas.

In vitro culture from mature seeds of Passiflora species

The genus Passiflora comprises hundred species, mainly native of the South American tropics and rainforests, which are grouped into 21 subgenera. Some species are widely studied for their economic importance and are chiefly cultivated for production of fruit juice. To obtain a continuous source of material for a screening of secondary metabolites, zygotic embryo culture was attempted for 62 Passiflora species, starting from seeds mainly collected in the wild. Twenty nine of these species produced calli, which had very different growth rates. Plants were successfully regenerated from calli of 13 different species. For 25 of the responsive species this is the first report of in vitro culture.

O gênero Passiflora compõe centenas de espécies, a maioria de origem dos trópicos e das florestas da América do Sul, as quais são agrupadas em 21 subgêneros. Algumas espécies foram intensamente estudadas por sua importância econômica e são cultivadas principalmente para a produção de suco de fruta. Cultura de 29 espécies de Passiflora foram obtidos a partir de embriões zigóticos e de culturas de endosperma. Foram obtidos diferentes tipos de calos de crescimento, de tal forma que plantas foram regeneradas a partir de calos de 13 espécies diferentes. Não haviam sido ainda relatadas culturas in vitro para 25 das espécies trabalhadas.