Flooding is an environmental stress for many natural and man-made ecosystems worldwide. Genetic diversity in the plant response to flooding includes alterations in architecture, metabolism, and elongation growth associated with a low O2 escape strategy and an antithetical quiescence scheme that allows endurance of prolonged submergence. Flooding is frequently accompanied with a reduction of cellular O2 content that is particularly severe when photosynthesis is limited or absent. This necessitates the production of ATP and regeneration of NAD+ through anaerobic respiration. The examination of gene regulation and function in model systems provides insight into low-O2-sensing mechanisms and metabolic adjustments associated with controlled use of carbohydrate and ATP. At the developmental level, plants can escape the low-O2 stress caused by flooding through multifaceted alterations in cellular and organ structure that promote access to and diffusion of O2. These processes are driven by phytohormones, includin...

Flooding Stress: Acclimations and Genetic Diversity

Rice ( Oryza sativa L.) is a principal source of food for more than half of the world population, especially in South and Southeast Asia and Latin America. Elsewhere, it represents a high‐value commodity crop. Change in the method of crop establishment from traditional manual transplanting of seedlings to direct‐seeding has occurred in many Asian countries in the last two decades in response to rising production costs, especially for labor and water. Direct‐seeding of rice (DSR) may involve sowing pregerminated seed onto a puddled soil surface (wet‐seeding) or into shallow standing water (water‐seeding), or dry seed into a prepared seedbed (dry‐seeding). In Europe, Australia, and the United States, direct‐seeding is highly mechanized. The risk of crop yield loss due to competition from weeds by all seeding methods is higher than for transplanted rice because of the absence of the size differential between the crop and weeds and the suppressive effect of standing water on weed growth at crop establishment. Of 1800 species reported as weeds of rice, those of the Cyperaceae and Poaceae are predominant. The adoption of direct‐seeding has resulted in a change in the relative abundance of weed species in rice crops. In particular, Echinochloa spp., Ischaemum rugosum, Cyperus difformis , and Fimbristylis miliacea are widely adapted to conditions of DSR. Species exhibit variability in germination and establishment response to the water regime postsowing, which is a major factor in interspecifically selecting constituents of the weed flora. The relatively rapid emergence of “weedy” (red) rice, rice phenotypically similar to cultivars but exhibiting undesirable agronomic traits, has been observed in several Asian countries practicing DSR, and this poses a severe threat to the sustainability of the production system. Stale seedbeds, tillage practices for land leveling, choice of competitive rice cultivars, mechanical weeders, herbicides, and associated water management are component technologies essential to the control of weeds in DSR. Herbicides in particular are an important tool of weed management, but hand weeding is either partially or extensively practiced in countries of Asia, Africa, and Latin America. Though yet to be globally commercialized, transgenic rice varieties engineered for herbicide resistance are a potential means of weed control. The release of herbicide‐resistant rice for red rice control in the United States has indicated the need to critically examine mitigation methods for the control of gene flow. Integrating preventive and interventional methods of weed control remains essential in managing weed communities in DSR, both to prohibit the evolution of herbicide resistance and to maximize the relative contributions of individual components where herbicides are not widely used. There remains a need to further develop understanding of the mechanisms and dynamics of rice weed competition and of the community dynamics of weed populations in DSR to underpin sustainable weed management practices.

Weed Management in Direct‐Seeded Rice

Submergence-1 (Sub1), a major quantitative trait locus affecting tolerance to complete submergence in lowland rice (Oryza sativa), contains two or three ethylene response factor (ERF)-like genes whose transcripts are regulated by submergence. In the submergence-intolerant japonica cultivar M202, this locus encodes two ERF genes, Sub1B and Sub1C. In the tolerant near-isogenic line containing the Sub1 locus from the indica FR13A, M202(Sub1), the locus additionally encodes the ERF gene Sub1A. During submergence, the tolerant M202(Sub1) displayed restrained leaf and internode elongation, chlorophyll degradation, and carbohydrate consumption, whereas the enzymatic activities of pyruvate decarboxylase and alcohol dehydrogenase were increased significantly compared with the intolerant M202. Transcript levels of genes associated with carbohydrate consumption, ethanolic fermentation, and cell expansion were distinctly regulated in the two lines. Sub1A and Sub1C transcript levels were shown to be upregulated by submergence and ethylene, with the Sub1C allele in M202 also upregulated by treatment with gibberellic acid (GA). These findings demonstrate that the Sub1 region haplotype determines ethylene- and GA-mediated metabolic and developmental responses to submergence through differential expression of Sub1A and Sub1C. Submergence tolerance in lowland rice is conferred by a specific allele variant of Sub1A that dampens ethylene production and GA responsiveness, causing quiescence in growth that correlates with the capacity for regrowth upon desubmergence.

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A variable cluster of ethylene response factor-like genes regulates metabolic and developmental acclimation responses to submergence in rice.

Biodiversity is a challenging field of research. Approaches are manifold and mostly cover few aspects of the total wealth of phenomena only. The mapping of the vascular plants and the inventory of Basidiomycota in Bavaria are projects to be mentioned in this context as one part of the commitment of the author. In the following article the author describes further activities during his lifework in regard A. Bresinsky (*) Institute of Botany of University of Regensburg, D-93040, Regensburg, Germany e-mail: abresinsky@t-online.de U. Lüttge et al. (eds.), Progress in Botany, Progress in Botany 75, DOI 10.1007/978-3-642-38797-5_1, © Springer-Verlag Berlin Heidelberg 2014 3 to ant–plant interactions resulting in dispersal and distribution of plants, and moreover, in respect to speciation and to evolution of high ranked taxa within the fungi, discussed mainly in relation to the genus Pleurotus and the order Boletales. In fungi the investigations include breeding systems, isolation barriers, polyploidy, pigment patterns and DNA phylogeny. The pigment patterning in Boletales correlates well with the phylogeny as revealed by DNA analysis of selected gene sections.

Progress in Botany

Rice is the principle staple crop of Asia and any deterioration of rice production systems through climate change would seriously impair food security in this continent. This review assesses spatial and temporal vulnerabilities of different rice production systems to climate change impacts in Asia. Initially, the review discusses the risks of increasing heat stress and maps the regions where current temperatures are already approaching critical levels during the susceptible stages of the rice plant, namely Pakistan/north India (Oct.), south India (April, Aug.), east India/Bangladesh (March-June), Myanmar/Thailand/Laos/Cambodia (March-June), Vietnam (April/Aug.), Philippines (April/June), Indonesia (Aug.) and China (July/Aug.). Possible adaptation options for heat stress are derived from regions where the rice crop is already exposed to very high temperatures including Iran and Australia. Drought stress is also expected to aggravate through climate change; a map superimposing the distribution of rainfed rice and precipitation anomalies in Asia highlights especially vulnerable areas in east India/Bangladesh and Myanmar/Thailand. Then, the review gives emphasis to two rice growing environments that have outstanding importance for food supply in Asia and, at the same time, are particularly vulnerable to climate impacts. The mega-deltas in Vietnam, Myanmar and Bangladesh are the backbone of the rice economy in the respective country and will experience specific climate change impacts due to sea level rise. Significant improvements of the rice production systems, that is, higher resilience to flooding and salinity, are crucial for maintaining or even increasing yield levels in these very productive deltaic regions. The other ‘hotspot’ with especially high climate change risks in Asia is the Indo-Gangetic Plains (IGP) which will be affected by the melting of the Himalayan glaciers. The dominant land use type in the IGP is rice-wheat rotation, and we discuss specific vulnerabilities and possible adaptation options in the different sub-regions of the IGP. We conclude that geo-spatial vulnerability assessments may become crucial for planning targeted adaptation programs, but that policy frameworks are needed for their implementation.

Regional vulnerability of climate change impacts on Asian rice production and scope for adaptation

Elongation ability and non-structural carbohydrate levels in relation to submergence tolerance in rice

Submergence tolerance in relation to variable floodwater conditions in rice

Summary. The activities of antioxidant enzymes and levels of antioxidants involved in oxygen detoxification were studied in seedlings of three indica rice (Oryza sativa L.) cultivars, namely Panikekoa and T 1471 that show good capacity for anaerobic seedling establishment (tolerant reaction) and IR 42 which has a poor anaerobic seedling establishment capacity (susceptible reaction). The activities of the antioxidant enzymes tested decreased under submergence. The activity of glutathione reductase (GR, EC 1.6.4.2) was found to be more sensitive compared to the other enzymes. On the other hand, the activity of superoxide dismutase (SOD, EC 1.15.1.9) was comparatively stable. After 5 days of submergence tolerant cultivars maintained almost 3-fold higher glutathione reductase activity than the susceptible cultivar. During submergence the tolerant cultivars showed comparatively less ascorbic acid oxidase (AAO, EC 1.10.3.3) activity and had greater ascorbic acid content. The activities of superoxide dismutase, catalase (CAT, EC 1.11.1.6), peroxidase (POX, EC 1.11.1.7), ascorbic acid peroxidase (APX, EC 1.11.1.11) and polyphenol oxidase (PPO, EC 1.14.18.1) were also higher in tolerant cultivars during submergence compared to the susceptible cultivar. Submergence was found to induce aldehyde releasing capacity in rice seedlings which was more apparent in the susceptible cultivar.

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Antioxidant enzymes and aldehyde releasing capacity of rice cultivars (oryza sativa l.) as determinants of anaerobic seedling establishment capacity

Submergence tolerance in rice: Biophysical constraints physiological basis and Identification of Donors

The activities of starch hydrolyzing enzymes and phosphatases were studied in seedlings of three Indica rice (Oryza sativa L.) cultivars, namely Panikekoa & T 1471 that showed good capacity for seedling establishment under submergence (tolerant) and IR 42 which had poor under water seedling establishment capacity (susceptible). Under submergence the total amylolytic activities were significantly higher in susceptible cultivars compared to the tolerant cultivars. Likely, the activities of α-amylase, debranching enzymes and α-glucosidase were also higher in susceptible cultivar IR 42. The activities of starch phosphorylase were comparatively higher in tolerant cultivars than susceptible cultivars. Susceptible cultivars maintained higher activities of both acid and alkaline phosphatase as well as phytase activities. Tolerant cultivars with higher seed biomass and low activity of hydrolytic enzymes might sustain the supply of food materials for longer period and hence, survived and established themselves under water.

Krishna Kaveri Das

Papers

Elongation ability and non-structural carbohydrate levels in relation to submergence tolerance in rice

Submergence tolerance in relation to variable floodwater conditions in rice

Antioxidant enzymes and aldehyde releasing capacity of rice cultivars (oryza sativa l.) as determinants of anaerobic seedling establishment capacity

Submergence tolerance in rice: Biophysical constraints physiological basis and Identification of Donors

Role of starch hydrolytic enzymes and phosphatases in relation to under water seedling establishment in rice