Effect of Half and Whole Root Drying on Photosynthesis, Nitrate Concentration, and Nitrate Reductase Activity in Roots and Leaves of Micropropagated Apple Plants

Abstract

<jats:p>Half or whole root systems of micropropagated `Gala' apple (<jats:italic>Malus ×domestica</jats:italic> Borkh.) plants were subjected to drought stress by regulating the osmotic potential of the nutrient solution using polyethylene glycol (20% w/v) to investigate the effect of root drying on NO<jats:sub>3</jats:sub>- content and metabolism in roots and leaves and on leaf photosynthesis. No significant difference in predawn leaf water potential was found between half root stress (HRS) and control (CK), while predawn leaf water potential from both was significantly higher than for the whole root stress (WRS) treatment. However, diurnal leaf water potential of HRS was lower than CK and higher than WRS during most of the daytime. Neither HRS nor WRS influenced foliar NO<jats:sub>3</jats:sub>- concentration, but both significantly reduced NO<jats:sub>3</jats:sub>- concentration in drought-stressed roots as early as 4 hours after stress treatment started. This reduced NO<jats:sub>3</jats:sub>- concentration was maintained in HRS and WRS roots to the end of the experiment. However, there were no significant differences in NO<jats:sub>3</jats:sub>- concerntation between CK roots and unstressed roots of HRS. Similar to the effect on root NO<jats:sub>3</jats:sub>- concentration, both HRS and WRS reduced nitrate reductase activity in drought-stressed roots. Moreover, leaf net photosynthesis, stomatal conductance and transpiration rate of HRS plants were reduced significantly throughout the experiment when compared with CK plants, but the values were higher than those of WRS plants in the first 7 days of stress treatment though not at later times. Net photosynthesis, stomatal conductance and transpiration rate were correlated to root NO<jats:sub>3</jats:sub>- concentration. This correlation may simply reflect the fact that water stress affected both NO<jats:sub>3</jats:sub>- concentration in roots and leaf gas exchange in the same direction.</jats:p>

Partial Rootzone Drying to Save Water While Growing Apples in a Semi‐arid Region

“…The E was reduced, on average, by 5.9% and 9.7% in 2006 and 2007, respectively (Table II). Therefore, rather than being regulated by signals from the roots, our data suggest that even in plants exposed to PRD, g s is controlled by the Ψ leaf (Tan and Buttery, 1982); (Zhao et al, 2006) in a similar fashion as in plants exposed to water deficit (Steudle, 2001). This is consistent with previous PRD apple experiments conducted in humid areas of New Zealand, where air vapour pressure deficit is much lower than in a semi-arid region (Zegbe et al, 2007); .…”

Fisiologia da produção de mudas cítricas sob deficiência hídrica

“…Pesquisas acerca de respostas fisiológicas de plantas sob deficiência hídrica utilizam freqüentemente osmólitos artificiais adicionados ao substrato por meio de soluções nutritivas, uma vez que estas substâncias permitem fixar um determinado potencial da água no meio por tempo indeterminado, o que não pode ser reproduzido pela interrupção natural da irrigação (ZEKRI;PARSONS, 1990). Um dos principais osmólitos empregados nesses casos é o polietileno glicol ou PEG (AHMAD; JAVED; ASHRAF, 2007;FALTENOVICH;WELBAUM, 2008;KOCHEVA et al, 2007;ZHAO et al, 2006). O PEG consiste em um polímero de óxido de etileno de cadeia longa (C 2n+2 H 4n+6 O n+2 ), inerte e não iônico, comercializado em diferentes pesos moleculares (STEUTER; MOZAFAR; GOODIN, 1981), cuja ação é atribuída ao bloqueio da absorção de água e conseqüente dessecação da planta (LAWLOR, 1970).…”