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Abstract: Barley seedlings were grown in pots in controlled environment chambers and progressive drought treatments were imposed 11d after sowing. Soil water content decreased from 92 to 10% following 14d without watering. Increases of biomass in shoots and roots slowed after 4 and 9d of water stress, respectively. Thirty barley root metabolites were monitored in this study and 85% were significantly altered by drought. Sucrose, raffinose, glucose, fructose, maltose, malate, asparagine and proline increased and myo-inositol, glycerate, alanine, serine, glycine and glutamate decreased during drought. Primary metabolism was likely involved in various crucial processes during water stress including, osmotic adjustment, nitrogen sequestration and ammonia detoxification. Rates of photosynthesis and stomatal conductance recovered in 2d and shoot growth commenced the 3rd day after rehydration. Root growth also exhibited a lag after rehydration but this was attributed to high nutrient concentrations during water stress. Malate and proline recovered within 1d but serine was only partially reversed 6d after rehydration. Malate, aspartate and raffinose decreased below well-watered, control levels following rehydration. Variation in the magnitude and time necessary for individual compounds to fully recover after rehydration suggested the complexity of metabolic processes initiated by re-watering. [Copyright &y& Elsevier]

Abstract: Responses of soluble amino acids and organic acids to either ambient (36Pa) or elevated (100Pa) CO2 treatments were determined using barley primary leaves (Hordeum vulgare L. cv. Brant). Total soluble amino acids were increased 33% by CO2 enrichment 9 days after sowing (DAS), but a decrease relative to the ambient CO2 treatment was observed with increasing leaf age. Marked declines of glutamine and asparagine were observed under CO2 enrichment, both diurnally and with advancing leaf age. Consequently, total soluble amino acids were 59% lower in the elevated compared to the ambient CO2 treatment 17 DAS. It was likely that chlorosis in response to CO2 enrichment negatively impacted soluble amino acid levels in older barley primary leaves. In contrast to the ambient CO2 treatment, glutamine and most other soluble amino acids decreased as much as 60% during the latter half of a 12h photoperiod in primary leaves of 13-day-old seedlings grown under enhanced CO2. Malate was decreased about 9 percent by CO2 enrichment and citrate and succinate were increased by similar amounts when measured 9 and 13 DAS. Malate accumulation was also decreased about 20% by CO2 enrichment on a diurnal basis. The onset of CO2-dependent leaf yellowing had much less of an effect on organic acids than on soluble amino acids. This above results emphasized the sensitivity of N metabolism to CO2 enrichment in barley. Increased levels of citrate and succinate in response to CO2 enrichment suggested that the tricarboxylic acid cycle was upregulated in barley by CO2 enrichment. In summary, organic and amino acid levels in barley primary leaves were dynamic and were altered by age, diurnally and in response to CO2 enrichment. [Copyright &y& Elsevier]

Studies leaf yellowing in Barley. Effects of carbon dioxide (CO2) on photosynthetic electron-transport system; Impact of chlorosis and other forms of leaf injury on plant growth; Development of stunted, brittle and discolored leaves; Implications of leaf abnormalities; Susceptability of photosystem-II to light damage during CO2 elevation.

Net rates of carbon assimilation per unit leaf area by fully expanded, vegetative leaves of diploid (2 ×) and autotetraplloid (4 ×) barley (Hordeum vulgare L. cultivars OAC-21 and Brant) were not! significantly different (90% level) when measured under controlled environment conditions with air levels of. CO2 and either 2 or 20% O2. Leaf thickness. increased with ploidy so that net photosynthetic rates measured on single leaves were lower for 4 × than 2 × barley varieties when, compared on a dry or fresh weight basis. Rates of 14CO2 fixation by isolated mesophyll protoplasts prepared from seedlings were also lower for 4× than 2× varieties about 108 and 125 μmol (mg Chl)-1 h-1, respectively]. Carbohydrate accumulation in leaves of 5-week- old plants averaged 28% (2×) and 47% (4×) of the total photosynthetic weight gain during the first 9 h of the light period. Estimated photoassimilate export from leaves was 15% (OAC-21) and 38% (Brant) lower for 4× compared to 2× isolines. The sucrose and oligofructan content of 4× compared to 2× leaves increased as a result of decreased photosynthate transport. Total tiller dry weight of plants raised in a glasshouse was greater for 4× than 2× barley varieties at ear emergence, but tiller height decreased with increasing ploidy. The nonstructural carbohydrate content of the inflorescence, leaves and lower stem organs was significantly (P ≤ 0.01) higher in 4× than in 2 × lines at this sampling. During the first 15 days of grain development total tiller dry weight increased by 46% (2 ×) compared to 8%. (4 ×) when the results of both varieties were averaged together. The dry weight gain of the ear during this period was about 60 to 8.0% lower for 4× compared to 2× isolines. The nonstructural carbohydrate content of the inflorescence was also about 24% (Brant) and 51% (OAC-21) lower for 4× as compared to 2× plants 15 days post ear emergence. The above results suggested that photosynthate partitioning, in autotetraploid barley was sink-limited. [ABSTRACT FROM AUTHOR]

Discusses the development of chlorosis in primary leaves of barley plants (Hordeum valgare L.) grown in ambient and twice-ambient carbon dioxide partial pressures. When leaf yellowing was observed; Extent of leaf yellowing; Photsynthetic rates of detached barley primary leaves; How chlorosis develops in primary leaves of barley plants.

The photosynthetic response of barley (Hordeum vulgare L. cv. Brant) primary leaves was studied as a function of chlorosis induced by CO2 enrichment. Leaf yellowing, measured as changes of chlorophyll a and b, was more extensive in controlled environments at elevated (680 ± 17 µl l−1) than at ambient (380 ± 21 µl l−1) CO2. Stomatal conductance of primary leaves was decreased by growth in elevated CO2 between 11 and 18 days after sowing (DAS) when measured at both 380 and 680 µl l−1 CO2. Internal leaf CO2 concentration (Ci) was also lower for elevated‐ compared to ambient‐CO2‐grown primary leaves between 11 and 14 DAS. Results suggest that non‐stomatal factors were responsible for the decreased photosynthetic rates of elevated‐ compared to ambient‐CO2‐grown primary leaves 18 DAS. Various photochemical measurements, including quantum absorptance (α), minimal (F0), maximal (Fm), and variable (Fv) chlorophyll fluorescence, as well as the Fv/Fm ratio, were significantly decreased 18 DAS in the elevated‐ compared to ambient‐CO2 treatment. Photochemical (qP) and nonphotochemical (qN) chlorophyll fluorescence quenching coefficients of 18‐day‐old primary leaves did not differ between CO2 treatments. Photosynthetic electron transport rates of photosystem II were slightly lower for elevated‐ compared to ambient‐CO2‐grown primary leaves 18 DAS. Concentrations of α‐amino N (i.e. free amino acids) in barley primary leaves were increased by CO2 enrichment 10 DAS, but subsequently, α‐amino N decreased in association with photosynthetic decline. Total acid protease activity was greater in elevated‐ than in ambient‐CO2‐grown leaves 18 DAS. The above findings suggest that photoinhibition and premature senescence were factors in the CO2‐dependent yellowing of barley primary leaves. [ABSTRACT FROM AUTHOR]

Oxygen evolution and chlorophyll fluorescence were measured in cold-hardened and unhardened leaves of barley (Hordeum vulgare L. cv. Åsa) during the induction period of photosynthesis. The lag phase of light-saturated photosynthesis was increased and steady-state rates of photosynthesis were higher in cold-hardened than in unhardened barley leaves. Fluorescence was quenched more rapidly during the first minutes of induction in hardened than unhardened leaves, largely because of greater energy-dependent quenching (qE). Also, slow fluorescence transients through the M peak were delayed and less pronounced in cold-hardened than in unhardened leaves. Based upon the combined fluorescence and oxygen evolution data it was concluded that cold-hardening delayed light activation of the energy consuming carbon reduction cycle, thereby delaying the use of ATP and NADPH formed in the light reaction. Measurements of oxygen evolution and fluorescence kinetics during photosynthetic induction under oxygenic and anoxygenic conditions suggest that oxygen photoreduction is important for additional ATP generation during both the onset of photosynthetic carbon assimilation and during steady-state photosynthesis. [ABSTRACT FROM AUTHOR]

Non‐structural storage carbohydrates were measured in 9‐day‐old barley (Hordeum vulgare L. cv. Brant) primary leaves. Accumulation rates of starch, sucrose and total non‐structural carbohydrates (TNC) were approximately linear when measured between 2‐ and 12‐h of light. Progressively higher TNC accumulation rates were observed at higher irradiance levels (i.e., comparing 250, 550 and 1050 ·mol m−2 s−1). Synthesis of a low‐molecular‐weight fructan also was enhanced by high irradiances. Low irradiance treatments decreased leaf sucrose levels and there was a corresponding increase in the lag period preceding starch synthesis in the light. Increased starch accumulation rates were usually observed when sucrose concentrations were high. These and other results suggested that cytosolic sucrose concentrations affected starch metabolism in the chloroplast. However, sucrose accumulation rates increased and starch storage decreased when barley seedlings were transferred from 20 to 10°C during the light period. Lowering the night temperature from 20 to 10°C for a single dark period 8‐days after planting increased the TNC content of barley primary leaves at the beginning of day nine. In this experiment, TNC accumulation rates of treated and untreated leaves were similar. Changes in the accumulation rate of TNC were usually observed within 2‐ to 4‐h after barley seedlings were exposed to altered environmental conditions. Monitoring rapid changes in leaf carbohydrate levels is a sensitive method for assessing the effects of environmental treatments on photosynthetic metabolism. [ABSTRACT FROM AUTHOR]