Efeito da temperatura e do teor de umidade na iniciação e desenvolvimento do rizoma de Kohleria eriantha (Benth.) Hanst. (Gesneriaceae)

Kohleria eriantha (Benth.) Hanst is a plant belonging to the family Gesneriaceae, with an underground organ, which is associated with vegetative reproduction. This organ is a rhizome, whose stem bears buds covered with modified leaves that store up starch. In small sections of this rhizome, containing six buds (1.5 to 2.0cm long), only one bud sprouted. The sprouted bud could be differentiated into two morphological pattern: aerial part or rhizome. Sprouting of the rhizome pattern occurred in sections kept on substrate with low water content (1mL of water), or lacking water, whereas sprouting of the aerial part pattern occurred in sections on substrate with high water content (12mL of water). Temperature at 20ºC also stimulated sprouting of the rhizome pattern, regardless of the water volume in the substrate. Sprouting of the rhizome pattern occurred still in sections on substrate to which polyethylene glycol 6000 (PEG) solution was added at the concentrations of 161.2, 235.2 and 340.0g/L, resulting in potentials of -3, -6 and -12 MPa, respectively. Sections kept on substrate with low water content (1 ml of water) showed a reduction in the dry matter content and high osmotic concentration in comparison with those on substrate with high water content. The results obtained revealed that forming of the rhizome pattern was influenced by water content and temperature. It is suggested that sprouting of the rhizome pattern was induced by the low water potential in the sections, when kept on substrate with low water content. Moreover, it was observed that the rhizome buds of Kohleria eriantha showed a high degree of plasticity.

Physiological limitations in two sugarcane varieties under water suppression and after recovering

Increasing water scarcity and depleted water productivity in irrigated soils are inducing farmers to adopt improved varieties, such as those with high-capacity tolerance. The use of tolerant varieties of sugarcane might substantially avoid the decline of productivity under water deficit. This research aimed to evaluate the harmful effects of drought on the physiology of two sugarcane varieties (RB867515 and RB962962) during the initial development. Young plants were subjected to irrigation suspension until total stomata closure, and then rewatered. Significant reduction on stomatal conductance, transpiration, and net photosynthesis were observed. RB867515 showed a faster stomatal closure while RB962962 slowed the effects of drought on the gas exchanges parameters with a faster recovering after rewatering. Accumulation of carbohydrates, amino acids, proline, and protein in the leaves and roots of the stressed plants occurred in both varieties, substantially linked to reduction of the leaf water potential. Due to the severity of stress, this accumulation was not enough to maintain the cell turgor pressure, so relative water content was diminished. Water stress affected the contents of chlorophyll (a, b, and total) in both varieties, but not the levels of carotenoids. There was a significant reduction in dry matter under stress. In conclusion, RB962962 variety endured stressed conditions more than RB867515, since it slowed down the damaging effects of drought on the gas exchanges. In addition, RB962962 presented a faster recovery than RB867515, a feature that qualifies it as a variety capable of enduring short periods of drought without major losses in the initial stage of its development.