The Role of Aquaporins and Membrane Damage in Chilling and Hydrogen Peroxide Induced Changes in the Hydraulic Conductance of Maize Roots  

Abstract

When chilling-sensitive plants are chilled, root hydraulic conductance (L o ) declines precipitously; L o also declines in chillingtolerant plants, but it subsequently recovers, whereas in chilling-sensitive plants it does not. As a result, the chilling-sensitive plants dry out and may die. Using a chilling-sensitive and a chilling-tolerant maize genotype we investigated the effect of chilling on L o , and its relationship to osmotic water permeability of isolated root cortex protoplasts, aquaporin gene expression, aquaporin abundance, and aquaporin phosphorylation, hydrogen peroxide (H 2 O 2 ) accumulation in the roots and electrolyte leakage from the roots. Because chilling can cause H 2 O 2 accumulation we also determined the effects of a short H 2 O 2 treatment of the roots and examined the same parameters. We conclude from these studies that the recovery of L o during chilling in the chilling-tolerant genotype is made possible by avoiding or repairing membrane damage and by a greater abundance and/or activity of aquaporins. The same changes in aquaporins take place in the chilling-sensitive genotype, but we postulate that membrane damage prevents the L o recovery. It appears that the aquaporin response is necessary but not sufficient to respond to chilling injury. The plant must also be able to avoid the oxidative damage that accompanies chilling.Many crop species such as maize (Zea mays) that originate in tropical regions are sensitive to low temperatures and grow poorly after exposure to a cold period (Miedema, 1982). Below 12°C to 14°C, maize seedlings are damaged as a result of leaf dehydration and an inhibition of photosynthesis. Such damage may result in the plant's death (Miedema, 1982). With the wide utilization in temperate climates of crops of tropical origin, the adverse effect of chilling is an important agricultural problem the physiological basis of which can be elucidated. Cold-tolerant species increase their root hydraulic conductance (L o ) during low temperature periods (Fennell and Markhart, 1998;Bigot and Boucaud, 2000), and the same phenomenon has been observed in a chilling-tolerant genotype of maize (Aroca et al., 2001b(Aroca et al., , 2003b. The water deficit in the aerial parts of a chilling-sensitive maize genotype is caused in part by low temperature inhibition of L o (Aroca et al., 2001b(Aroca et al., , 2003b. The recovery of L o in cold-tolerant plants may be associated with an increase in the activity or the abundance of aquaporins in the plasma membranes of root cells. On the other hand, the opposite may happen in cold-sensitive species: aquaporins may be down-regulated or inactivated (Aroca et al., 2001b;Sanders and Markhart, 2001;). Lee et al. (2004b) recently showed that in cucumber (Cucumis sativus), a cold sensitive species, a brief exposure to low temperature reduces root pressure, hydraulic conductivity, and active nutrient transport. These authors also postulated that changes in the activity of aquaporins underlie the changes in hydraulic conductivity.Response to cold,...

Water relations and an expression analysis of plasma membrane intrinsic proteins in sensitive and tolerant rice during chilling and recovery

“…At the mRNA level, decreased expression of individual PIP genes during chilling was observed in rice [19,7], maize [6] and Arabidopsis [20]. We determined the expression of all the 11 PIP genes by real-time RT-PCR using TaqMan-MGB probes, and found that chilling reduced the expression of most PIP genes in our experiments (Figure 3), a result consistent with a previous report [7].…”

“…In this study, chilling led to a dramatic decrease in osmotic root Lp in Somewake and Wasetoitsu ( Figure 2C), an observation that paralleled observations in maize [3,6], spinach [9], bean [8], cucumber and figleaf gourd [12]. The water imbalance was probably triggered by the sharp drop in root water uptake at the onset of chilling, whereas decreased transpiration occurred later ( Figure 2B).…”

“…Many reports have emphasized the changes in water relations because water homeostasis is essential for plant survival under this stress condition, and a significant symptom of chilling injury is shoot water deficit resulting from imbalance between water transport and transpiration [2]. It has been well documented that root water transport is sharply suppressed by exposure to low temperature in a number of species, including maize [3][4][5][6], rice [7], bean [8], spinach [9], aspen [10], cucumber and figleaf gourd [11,12]. Some studies have also demonstrated that a decrease in transpiration follows the reduction in root water flow [5,10].…”

“…Aquaporins have previously been reported to be involved in chilling responses [4,19] but only recently have comprehensive analysis of aquaporin expression at the mRNA level in response to low temperature been done. Techniques used were Northern blot, semi-quantitative reverse transcription (RT)-PCR and real-time RT-PCR using SYBR green dye in species such as Arabidopsis [20], maize [6] and rice [7]. Comparative analysis between cucumber (chilling sensitive) and figleaf gourd (chilling resistant) indicated that the decrease in cell hydraulic conductivity (Lp) at low temperature was associated with the open/close state of water channels [11,12].…”

“…Comparative analysis between cucumber (chilling sensitive) and figleaf gourd (chilling resistant) indicated that the decrease in cell hydraulic conductivity (Lp) at low temperature was associated with the open/close state of water channels [11,12]. However, in chilling-sensitive maize, the decrease in root Lp upon chilling was due to oxidative damage to the membranes rather than a decrease in aquaporin amount or a change in phosphorylation status [6]. The roles of aquaporins in plant chilling tolerance remain elusive.…”