Sugar and fructan accumulation during metabolic adjustment between respiration and fermentation under low oxygen conditions in wheat roots.

In terms of gene expression and carbohydrate metabolism, the response of wheat seedlings to hypoxia is dramatically different from the anoxic response. Total carbohydrate content of roots increased 4-fold during 6 days of hypoxia, with a 17-fold increase in fructans. In contrast, anoxically treated roots depleted all soluble carbohydrates and died within 72 h. Gas exchange measurements (CO(2) release vs. O(2) uptake) demonstrate that hypoxia establishes a new balance between fermentation and aerobic respiration in the roots without altering the flux of carbon through glycolysis. Furthermore, the respiratory component of this new balance is 55% higher in roots that have been hypoxically pretreated compared to non-hypoxically pretreated roots. The establishment of this new homeostasis under hypoxia involves the induction of glycolytic (aldolase and enolase) and fermentative enzymes (pyruvate decarboxylase, alcohol dehydrogenase, and lactate dehydrogenase). Enzyme induction is generally complete within 24 h with mRNA induction occurring primarily during Period I (0-6 h of hypoxia), and maximal enzymes activities attained during Period II (6-24 h of hypoxia). Accumulation rates of Suc, hexoses, and fructans also change during Periods I and II. By the start of Period III (24-144 h of hypoxia), the metabolic adjustments are complete and fructans are the major carbohydrate accumulated. In anoxia, the pattern of enzyme induction was dramatically different: aldolase was not induced and declined throughout the treatment. Alcohol dehydrogenase, pyruvate decarboxylase, and lactate dehydrogenase were induced as in hypoxia, but rapidly declined within 72 h of anoxia. Only enolase exhibited a similar expression pattern in both anoxia and hypoxia.

Short term effects of Glomus claroideum and Azospirillum brasilense on growth and root acid phosphatase activity of Carica papaya L. under phosphorus stress.

Arbuscular mycorrhizal fungi (AMF) are able to increase root enzymatic activity of acid and alkaline phosphatases. However, the role of AMF on phosphatase activity has not been reported in papaya (Carica papaya L.), which is frequently established at places with soil phosphorus (P) deficiencies. The goals of this research were to determine the effect of Glomus claroideum (Gc), and plant growth promoting rhizobacterium Azospirillum brasilense strain VS7 [Ab]) on root phosphatase activity and seedling growth of Carica papaya L. cv. Red Maradol under low P conditions. There were four treatments-colonization with: 1) Gc, 2) Ab, 3) Gc+Ab, and 4) non-inoculated seedlings. Plants were established in a coarse sand:sandy loam substrate under P-limitation (11 microg P ml(-1)), supplied with a modified Long Ashton Nutrient Solution. Seedling growth was severely reduced by low P. Gc+Ab inoculated plants had greater total dry matter and leaf area than non-colonized plants. Gc-inoculated plants had greater leaf area than non-colonized plants. Treatments did not differ in leaf area ratio, specific leaf area and, total chlorophyll content. There was a non-significant effect on stem relative growth rate with Gc and Gc+Ab plants. Mycorrhizal colonization enhanced the bacterial population 3.4-fold in the Gc+Ab treatment compared with the population quantified in Ab treatment. Soluble and extractable root acid phosphatase activity (RAPA) was higher in Gc inoculated plants. We discussed on the possible relation among both inoculated microorganisms and also with the P-limitation which plants were established.