The submergence-tolerance regulator, SUBMERGENCE1A (SUB1A), of rice (Oryza sativa L.) modulates gene regulation, metabolism and elongation growth during submergence. Its benefits continue during desubmergence through protection from reactive oxygen species and dehydration, but there is limited understanding of SUB1A's role in physiological recovery from the stress. Here, we investigated the contribution of SUB1A to desubmergence recovery using the two near-isogenic lines, submergence-sensitive M202 and tolerant M202(Sub1). No visible damage was detected in the two genotypes after 3 d of submergence, but the sublethal stress differentially altered photosynthetic parameters and accumulation of energy reserves. Submergence inhibited photosystem II photochemistry and stimulated breakdown of protein and accumulation of several amino acids in both genotypes at similar levels. Upon desubmergence, however, more rapid return to homeostasis of these factors was observed in M202(Sub1). Submergence considerably restrained non-photochemical quenching (NPQ) in M202, whereas the value was unaltered in M202(Sub1) during the stress. Upon reaeration, submerged plants encounter sudden exposure to higher light. A greater capability for NPQ-mediated photoprotection can benefit the rapid recovery of photosynthetic performance and energy reserve metabolism in M202(Sub1). Our findings illuminate the significant role of SUB1A in active physiological recovery upon desubmergence, a component of enhanced tolerance to submergence.

Water deficit is a major limiting factor for grass culture in many regions with physiological mechanisms of tolerance not yet well understood. Antioxidant isozymes and hormones may play important roles in plant tolerance to water deficit. This study was designed to investigate antioxidant enzymes, isozymes, abscisic acid (ABA), and indole-3-acetic acid (IAA) responses to deficit irrigation in two perennial ryegrass (Lolium perenne L.) cultivars contrasting in drought tolerance. The plants were subjected to well-watered {100% container capacity, 34.4% ± 0.21% volumetric moisture content (VWC), or deficit irrigation [30% evapotranspiration (ET) replacement; 28.6% ± 0.15% to 7.5% ± 0.12% VWC]} conditions for up to 8 days and rewatering for 4 days for recovery in growth chambers. Deficit irrigation increased leaf malondialdehyde (MDA) content in both cultivars, but drought-tolerant Manhattan-5 exhibited lower levels relative to drought-sensitive Silver Dollar. Superoxide dismutase (SOD) activity declined and then increased during water-deficit treatment. ‘Manhattan-5’ had higher SOD activity and greater abundance of SOD1 isozyme than ‘Silver Dollar’ under water deficit. Deficit irrigation increased catalase (CAT) and ascorbate peroxidase (APX) activity in ‘Manhattan-5’, but not in ‘Silver Dollar’. ‘Manhattan-5’ had higher CAT, APX, and peroxidase (POD) activity than ‘Silver Dollar’ during water limitation. Deficit irrigation increased mRNA accumulation of cytosolic cupper/zinc SOD (Cyt Cu/Zn SOD), whereas gene expression of manganese SOD (Mn SOD) and peroxisome APX (pAPX) were not significantly altered in response to deficit irrigation. No differences in Cyt Cu/Zn SOD, Mn SOD, and pAPX gene expression were found between the two cultivars under deficit irrigation. Water limitation increased leaf ABA and IAA contents in both cultivars, with Silver Dollar having a higher ABA content than Manhattan-5. Change in ABA level may regulate stomatal opening and oxidative stress, which may trigger antioxidant defense responses. These results indicate that accumulation of antioxidant enzymes and ABA are associated with perennial ryegrass drought tolerance. Activity and isozyme assays of key antioxidant enzymes under soil moisture limitation can be a practical screening approach to improve perennial ryegrass drought tolerance and quality.

The Colorado potato beetle is an important pest of solanaceous plants in the Northern Hemisphere. Better understanding of its physiological responses to temperature stress and their interactions with still-prevalent chemical control has important implications for the management of this insect. We measured mortality and expression of the Hsp70 heat shock proteins in the Colorado potato beetle larvae exposed to sublethal concentration of the commonly used insecticide imidacloprid, and to supraoptimal temperatures. Both turned out to be significant stress factors, although induction of Hsp70 by imidacloprid observed in the present study was low compared to its induction by the heat. The two factors also interacted with each other. At an extreme temperature of 43 °C, exposure to a sublethal dose of imidacloprid resulted in a significant rise in larval mortality, which was not observed at an optimal temperature of 25 °C. Heat-stressed larvae also failed to respond to imidacloprid by producing more Hsp70. These findings suggest that when field rates of insecticides become insufficient for killing the exposed beetles under optimal temperature conditions due to the evolution of resistance in beetle populations, they may still reduce the probability of resistant beetles surviving the heat shock created by using propane flamers as a rescue treatment.

Responses of wheat (Triticum aestivum) to complete submergence are not well understood as research has focused on waterlogging (soil flooding). The aim of this study was to characterize the responses of 2 wheat cultivars differing vastly in submergence tolerance to test if submergence tolerance was linked to shoot carbohydrate consumption as seen in rice. Eighteen-day-old wheat cultivars Frument (intolerant) and Jackson (tolerant) grown in soil were completely submerged for up to 19 days while assessing responses in physiology, gene expression, and shoot metabolome. Results revealed 50% mortality after 9.3 and 15.9 days of submergence in intolerant Frument and tolerant Jackson, respectively, and significantly higher growth in Jackson during recovery. Frument displayed faster leaf degradation as evident from leaf tissue porosity, chlorophyll , and metabolomic fingerprinting. Surprisingly, shoot soluble carbohydrates, starch, and individual sugars declined to similarly low levels in both cultivars by day 5, showing that cultivar Jackson tolerated longer periods of low shoot carbohydrate levels than Frument. Moreover, intolerant Frument showed higher levels of phytol and the lipid peroxidation marker malondialdehyde relative to tolerant Jackson. Consequently, we propose to further investigate the role of ethylene sensitivity and deprivation of reactive O species in submerged wheat.

Producers of orchardgrass (Dactylis glomerata L.) hay in the Mid-Atlantic US have experienced a reduction in regrowth vigor and a decline in the persistence of their swards. The common management practice for the region is to harvest the first growth of hay by cutting at 2.5–7.5 cm height in May or June. We hypothesize that high temperature and low cutting height interact to limit the regrowth rate. To test this, orchardgrass plants were cut to either 2.5 or 7.5 cm and then placed into environmentally controlled chambers with a constant temperature of 20 or 35°C. Stubble was harvested on days 0, 1, 3, and 11 following cutting and subjected to metabolite analysis. Photosynthetic parameters were measured in the regrown leaves on days 3 and 11, and regrowth biomass was recorded on day 11. Under optimal growth temperature (20°C), vegetative regrowth upon defoliation was significantly enhanced when more stubble tissue remained. However, this advantage was not observed under heat stress. Defoliation generally decreases the abundance of carbohydrate reserves in stubble. Interestingly, high temperature stimulated the accumulation of starch and ethanol-soluble carbohydrates in plants cut to 7.5 cm. The similar trends were also observed in protein, amino acids, nitrate, and ammonium. These responses were not pronounced in plants cut to 2.5 cm, presumably due to inhibited photosynthesis and photosystem II photochemistry. Overall, we anticipated that heat-activated metabolite accumulation is part of adaptive response to the stress. However, modified allocation of carbohydrate and nitrogen reserves leads to reduced vegetative regrowth upon defoliation. These data suggest that cutting height management for orchardgrass may be more effective for its regrowth vigor and productivity in cool seasons or when cool weather follows hay harvest.