Patterns of pinitol accumulation in soybean plants and relationships to drought tolerance

Previous studies indicate that methylated cyclitols are potentially important osmolytes in plants. In a search for genetic diversity for pinitol (D -3-O-methyl-chiro-inositol) accumulation in soybean (Glycine max (L.) Merr.), two- to three-fold differences in pinitol accumulation in leaf blades were found among Chinese plant introductions. Furthermore, it was found that genotypes that accumulated high concentrations of pinitol, when grown under well-watered conditions, had been selected for performance in regions of China having low rainfall. Among the carbohydrates analysed, pinitol accumulation was uniquely associated with adaptation to dry areas of China. A detailed study of pinitol accumulation in the soybean plant showed two- to three-fold gradients in pinitol concentration from the bottom to the top of the plant. The gradient shifted during plant development, with consistently higher concentrations of pinitol in the uppermost leaves. Pinitol accumulation was not correlated with activity of the key biosynthetic enzyme, inositol methyl transferase. This result and other lines of evidence indicated that shifting patterns of pinitol accumulation were due to translocation of the cyclitol from lower to upper nodes. Pinitol, proline, and sugars accumulated in leaf blades on soybean plants subjected to drought, but the molar concentration of pinitol in stressed plants was greater than the concentrations of proline or sugars. Although the mechanism by which pinitol participates in drought tolerance is not fully known, our results provide additional correlative evidence linking pinitol and drought tolerance in soybean.     

The distribution of organic and mineral components in leaves and stems of Ranunculus fluitans Lam.

The differences in chemical composition of leaves and stems of Ranunculus fluitans Lam. were investigated. Typical distribution of organic and inorganic compounds were generally found not to be influenced by factors as day-time, eutrophication, or age of the weed bed. Starch, sugars, amino acids, and organic acids were at a higher level in the stem, but inorganic cations and anions were accumulated in the leaf. The distribution pattern and the relative contents of individual sugars, acids, and inorganic ions are discussed in detail.     

Osmotic adaption in Australian mangroves

Young and old leaves of twenty-three mangrove species from northern Queensland (Australia) were investigated for their mineral ion and organic solute content. With a few exceptions, the Na⁺ and the Cl-concentrations calculated on the basis of plant water (p.w.) were close to that of seawater and showed little age-induced changes. In some species, especially in Ceriops tagal, SO₄ ^2- accumulated with increasing leaf age. The most widely distributed organic solutes were pinitol and mannitol, which were stored up to 280 mM plant water. A negative correlation between pinitol and SO₄ ^2- was found in the case of Ceriops tagal. Other compatible solutes known for halophytes, such as proline and methylated quaternary ammonium compounds (MQAC), were present only in a few mangrove species. Proline occurred in two Xylocarpus species, while MQAC were accumulated by Avicennia eucalyptifolia, A. marina, Acanthus ilicifolius, Heritiera littoralis and Hibiscus tiliaceus. In all other species, low molecular weight carbohydrates (LMWC) were the main organic solutes.     

Water Stress Induced Changes in the Amounts of Some Photosynthetic Assimilation Products and Respiratory Metabolites of Sunflower Leaves

Sunflower leaves, water-stressed under controlled conditions,contained greater amounts of amino acids as their water potentialdecreased, with glycine, serine, and glutamate increasing morethan alanine and aspartate. Proline accumulated only at severestress. Low O₂ concentration altered the amounts of amino acids,principally decreasing the amount of glycine and increasingserine. The changes in total pool size are related to previousresults on the accumulation of 14C and the specific activityof products. Photorespiration was large under water stress,where leaves accumulated carbon in glycine of low specific activity,and in 21% O₂, where both total amount and specific activityof glycine was greater than in 1.5% O₂. This suggests that thereare two pools of glycine, one controlled by O₂ and closely relatedto photosynthesis, the other non-photosynthetic and affectedby water stress. The organic acids suocinate, citrate, and fumarate increasedat small leaf-water potentials. Sucrose decreased in amountwith stress and was absent at the most severe stress; therewas less glucose and fructose. The amount of carbon lost fromsugars was similar to the amount accumulated in amino acidstogether with the carbon lost in respiration. It is concluded that stress decreased the flux of carbon fromphotosynthesis for the synthesis of amino acids and sugars butmore carbon from stored materials, principally sucrose, wasused in the production of organic acids and amino acids.     

Comparative effects of osmotic-, salt- and alkali stress on growth,photosynthesis, and osmotic adjustment of cotton plants

In this study, cotton seedlings were subjected to osmotic-, salt- and alkali stresses. The growth, photosynthesis, inorganic ions, and organic acids in the stressed seedlings were measured, to compare the mechanisms by which plants adapt to these stresses and attempt to probe the mechanisms by which plants adapt to high pH stress. Our results indicated that, at high stress intensity, both osmotic and alkali stresses showed a stronger injurious effect on growth and photosynthesis than salt stress. Cotton accumulated large amount of Na+ under salt and alkali stresses, but not under osmotic stress. In addition, the reductions of K⁺, NO₃ ⁻, and H₂PO₄ ⁻ under osmotic stress were much greater than those under salt stress with increasing stress intensity. The lack of inorganic ions limited water uptake and was the main reason for the higher injury from osmotic-compared to salt stress on cotton. Compared with salt- and alkali stresses, the most dramatic response to osmotic stress was the accumulation of soluble sugars as the main organic osmolytes. In addition, we found that organic acid metabolism adjustment may play different roles under different types of stress. Under alkali stress, organic acids might play an important role in maintaining ion balance of cotton; however, under osmotic stress, malate might play an important osmotic role.     

Leaf age effects on solute accumulation in water-stressed grapevines

The effects of leaf age on water relations, organic solute, and total ion accumulation were studied in mature and immature leaves of two-year-old grapevines (Vitis vinifera L., cv. Savatiano) grown under water stress conditions. Osmotic potential at full turgor decreased significantly in leaves of stressed plants, irrespective of leaf age, indicating the occurrence of an active osmotic adjustment. The apoplastic water fraction (A) increased during leaf ontogeny in both control and stressed plants. However, the values of A were lower in stressed plants. Starch concentration decreased significantly in both mature and immature leaves during the drought cycle, while the relative proportion of monosaccharides and sucrose was markedly different in immature leaves compared to mature. The accumulation of total inorganic ions, induced by drought, was also age dependent, increasing significantly with leaf age, while there were no significant differences in total amino acids content. Inorganic ions and carbohydrates seem to be the major component of osmotic adjustment in mature and immature grapevine leaves, respectively.     

Drought resistance and recovery in mature Bituminaria bituminosa var. albomarginata

Few studies have investigated the response of perennial legumes to drought stress (DS) and their ability, following rewatering, to regrow and restore photosynthetic activity. We examined these responses for two genotypes of drought‐tolerant tedera (Bituminaria bituminosa var. albomarginata) and one genotype of lucerne (Medicago sativa). Plants were grown outdoors in 1‐m deep PVC pots with a reconstructed field soil profile, regularly watered for 8 months (winter to mid‐summer), and then moved to a glasshouse where either watering was maintained or drought was imposed for up to 47 days, before rewatering for 28 days. Drought stress greatly decreased shoot dry matter (DM) production in both species. Lucerne plants showed severe leaf desiccation after 21 days of withholding water. Relative leaf water content (RWC = 42%) and midday leaf water potential (LWP = ?6.5 MPa) decreased in tedera in response to DS, whereas leaf angle (85°) and lateral root DM both increased. Proline and pinitol accumulated in tedera leaves during DS, and their concentration declined after rewatering. Nine days after rewatering, previously drought‐stressed tedera had similar RWC and LWP to well‐watered control plants. In tedera and lucerne, 28 days after rewatering, photosynthesis and stomatal conductance were greater than in the well‐watered controls. The lateral root DM for one tedera genotype decreased during the recovery phase but for lucerne, the lateral root DM did not change during either the drought or the recovery phases. Overall, the root systems in tedera showed greater plasticity in response to DS and rewatering than in lucerne. In conclusion, tedera and lucerne showed different physiological and morphological strategies to survive and recover from DS. Proline and soluble sugars may act as a carbon source for regrowth in tedera during recovery. In comparison with lucerne, tedera's more rapid recovery after rewatering should contribute to a greater aboveground DM yield under alternating dry and wet periods. Tedera genotypes are highly heterogeneous and selecting genotypes with enhanced concentrations of pinitol and proline could be a valuable tool to improve plant performance during DS and recovery.     

The role of organic and inorganic solutes in the osmotic adjustment of drought-stressed Jatropha curcas plants

This study aimed to assess the accumulation of organic and inorganic solutes and their relative contribution to osmotic adjustment in roots and leaves of Jatropha curcas subjected to different water deficit intensity. Plants were grown in vermiculite 50% (control), 40%, 30%, 20% and 10% expressed in gravimetric water content. The water potential, osmotic potential and turgor potential of leaves decreased progressively in parallel to CO₂ photosynthetic assimilation, transpiration and stomatal conductance, as the water deficit increased. However, the relative water content, succulence and water content in the leaves did not show differences between the control and stressed plants, indicating osmotic adjustment associated with an efficient mechanisms to prevent water loss by transpiration through stomatal closure. The K⁺ ions had greater quantitative participation in the osmotic adjustment in both leaves and roots followed by Na⁺ and Cl⁻, while the NO₃⁻ ion only showed minor involvement. Of the organic solutes studied, the total soluble sugars showed the highest relative contribution to the osmotic adjustment in both organs and its concentration positively increased with more severe water deficit. The free amino acids and glycinebetaine also effectively contributed to the osmotic potential reduction of both the root and leaves. The role of proline was quantitatively insignificant in terms of osmotic adjustment, in both the control and stressed roots and leaves. Our data reveal that roots and leaves of J. curcas young plants display osmotic adjustment in response to drought stress linked with mechanisms to prevent water loss by transpiration by means of the participation of inorganic and organic solutes and stomatal closure. Of all the solutes studied, soluble sugars uniquely display a prominent drought-induced synthesis and/or accumulation in both roots and leaves.     

Changes in photosynthesis,xanthophyll cycle,and sugar accumulation in two North Australia tropical species differing in leaf angles

Two tropical species of North Australia, Acacia crassicarpa and Eucalyptus pellita, have similar leaf size and leaf structure but different leaf angles. A. crassicarpa with near vertical leaf angle directly reduced photon absorption and leaf temperature (T _l) and had relatively high photosynthetic activity (P _max) and low xanthophyll cycle activity. In contrast, E. pellita with a small leaf angle exhibited high T _l, low P _max, and high activity of xanthophyll cycle which was useful for the dissipation of excessive energy and reduction of photoinhibition. In the dry season, contents of soluble sugars including pinitol, sucrose, fructose, and glucose in A. crassicarpa increased whereas larger amounts of only fructose and glucose were accumulated in E. pellita. Different sugar accumulation may be involved in osmotic adjustment of leaves during water stress that makes photosynthesis more efficient. The leaf angle may be critical for developing different protective mechanisms in these two tropical tree species that ensure optimal growth in the high irradiance and drought stress environment in North Australia.     

Water Potential and Stomatal Resistance of Sunflower and Soybean Subjected to Water Stress during Various Growth Stages

Plants of two varieties of soybean (Glycine max (L.) Merr.) and two varieties of sunflower (Helianthus annuus L.) were grown in controlled environments and subjected to water stress at various stages of growth. Leaf resistances and leaf water potentials were measured as stress developed. In soybeans the upper leaf surface had a higher resistance than the lower surface at all leaf water potentials and growth stages. Resistance of the upper surface began to increase at a higher water potential and increased more than the resistance of the lower surface. Resistances returned to prestress values 4 days after rewatering. In sunflowers upper and lower leaf surfaces had similar resistances at all water potentials and growth stages. Leaf resistances were higher in sunflower plants stressed before flowering than in those stressed later. Sunflower plants stressed to −16 bars recovered their prestress leaf resistance and water potential a few days after rewatering, but leaves of sunflower plants stressed to −23 bars died. Leaves of soybean and sunflower plants stressed before flowering suffered less injury than those of older plants and sunflowers stressed after flowering suffered more injury than soybeans.     

Effect of Zn deficiency on net photosynthetic rate, 14C partitioning,and oil accumulation in leaves of peppermint

Changes in growth, CO₂ exchange rate, and distribution of photosynthetically fixed ¹⁴CO2 into the primary photosynthetic metabolic pool (sugars, amino acids and organic acids) and essential oil accumulation were determined in leaves (leaf positions 1-6 from apex) of developing peppermint grown in a solution culture at Zn concentrations of 0 and 0.05 g m-3. There was a significant decrease in ¹⁴C incorporation in total, ethanol-soluble and ethanol-insoluble fractions in Zn deficient plants at all leaf positions. 14C incorporated in essential oil and in sugars were significantly higher in leaf pairs 1 to 3 than in leaf pairs 4 to 6. ¹⁴C incorporation into amino acids and organic acids was higher in all leaf pairs in Zn deficient plants. Statistical analysis showed a positive significant association between Zn content of leaf and ¹⁴C incorporation into ethanol-soluble fraction and sugars and a negative correlation with ¹⁴C incorporation into amino acids and organic acids. Hence the content of sugars in leaves significantly influences essential oil accumulation under Zn stress. This revised version was published online in September 2006 with corrections to the Cover Date.     

Influence of gibberellic acid on <Superscript>14</Superscript>CO<Subscript>2</Subscript> metabolism,growth, and production of alkaloids in <Emphasis Type="Italic">Catharanthus roseus</Emphasis>

Changes in growth parameters, carbon assimilation efficiency, and utilization of ¹⁴CO₂ assimilate into alkaloids in plant parts were investigated at whole plant level by treatment of Catharanthus roseus with gibberellic acid (GA). Application of GA (1 000 g m⁻³) resulted in changes in leaf morphology, increase in stem elongation, leaf and internode length, plant height, and decrease in biomass content. Phenotypic changes were accompanied by decrease in contents of chlorophylls and in photosynthetic capacity. GA application resulted in higher % of total alkaloids accumulated in leaf, stem, and root. GA treatment produced negative phenotypic response in total biomass production but positive response in content of total alkaloids in leaf, stem, and roots. ¹⁴C assimilate partitioning revealed that ¹⁴C distribution in leaf, stem, and root of treated plants was higher than in untreated and variations were observed in contents of metabolites as sugars, amino acids, and organic acids. Capacity to utilize current fixed ¹⁴C derived assimilates for alkaloid production was high in leaves but low in roots of treated plants despite higher content of ¹⁴C metabolites such as sugars, amino acids, and organic acids. In spite of higher availability of metabolites, their utilization into alkaloid production is low in GA-treated roots.     

The ecological adaptability of <Emphasis Type="Italic">Phragmites australis</Emphasis> to interactive effects of water level and salt stress in the Yellow River Delta

Soil salinity and waterlogging are two major environmental problems in estuarine wetlands. To prevent the typical wetland plants from degradation by soil salinization and salt waterlogging and more effectively use the plants to provide wetland ecosystem services, we examined the ecological adaptability of Phragmites australis, a characteristic plant species in the Yellow River Delta, to the interactive effects of water level and salt stress. The results showed that P. australis adapts to salt and water table stressed environments through slowing down the growth rate, maintaining the tiller number, and adjusting the biomass allocation of different organs. The highest plant height and the largest leaf area were at 0 cm water table treatment; the 0.5 % NaCl treatment increased the aboveground biomass; higher water table increased the fibrous root biomass allocation, but largely decreased the leaf biomass. The exclusion of toxic inorganic ions such as Na⁺ and Cl^? and the accumulation of organic solutes are also important mechanisms to aid survival in saline wetlands. On average 35.1 % of Cl^? and 53.9 % of Na⁺ accumulated in belowground organs. The study could provide fundamental guidance for wetland restoration projects and wetland sustainable use in coastal zones such as the Yellow River Delta.     

Effect of salinity on osmotic adjustment characteristics of <Emphasis Type="Italic">Kandelia candel</Emphasis>

To elucidate the osmotic adjustment characteristics of mangrove plants, inorganic ion and organic solute contents of intermediate leaves were investigated in 3-month-old Kandelia candel (L.) Druce seedlings during 45 days of NaCl treatments (0, 200, and 500 mM NaCl). The contents of Na⁺, Cl⁻, total free amino acids, proline, total soluble sugars, pinitol and mannitol increased to different degree by salinity, whereas, K⁺ content decreased by salinity compared with control. NaCl treatment induced an increase of inorganic ion contribution while a decrease of organic solute contribution. It was concluded that accumulating a large amount of inorganic ions was used as the main osmotic adjustment mechanism under salinity treatment. However, accumulation of organic osmolytes might be considered to play much more important role in osmoregulation under severe salinity (500 mM NaCl) than under moderate salinity (200 mM NaCl), thus the damage caused by high toxic ions (Na⁺ and Cl⁻) concentration in K. candel leaves could be avoided.     

Contribution of inorganic components to osmotic adjustment and leaf folding for drought tolerance in pearl millet

Pearl millet, Pennisetum glaucum , is capable of adapting to severely dry environmental conditions. In order to elucidate the mechanism of adaptation to highly dehydrated conditions, we selected both tolerant (IP8210) and susceptible (IP8949) accessions from a total of 15 pearl millet accessions and characterized their morphological and physiological responses to severe drought stress. When these selected accessions were stressed with a severe drought treatment, the leaves of IP8210 exhibited upright folding, a response that effectively reduces the evaporative surface area of the canopy. On the contrary, the leaves of IP8949 exhibited wilting and did not appear to adapt to the drought stress. In comparison with IP8949, the capacity of osmotic adjustment (OA) was greater in both younger leaves and stems of IP8210, while their decrease in relative water content was different. IP8210 accumulated higher concentrations of NO₃^– than IP8949 in response to drought stress. In addition to inorganic solutes, several organic components such as sucrose, glucose, quaternary ammonium compounds, and amino acids including proline were also accumulated. IP8210 tended to accumulate more amino acids, typically due to the accumulation of asparagine and proline, while IP8949 accumulated more soluble sugars. While it is possible that K⁺ and NO₃^– were the major components contributing to osmotic regulations, sugars and amino acids might also function as a cytoprotectant, in addition to their role as osmoprotectants. Collectively, these results demonstrate that the morphological adaptation of leaf folding, OA in both the younger leaves and the stem, and the accumulation of NO₃^– and amino acids during earlier stress period contribute to superior drought tolerance that was exhibited in IP8210 of pearl millet.     

Osmolyte Allocation in Response to Tylenchulus semipenetrans Infection,Stem Girdling,and Root Pruning in Citrus

Previous studies indicated that Tylenchulus semipenetrans infection reduced concentrations of inorganic osmolytes, (Na⁺, Cl⁻, K⁺), in roots, along with leaf K⁺ in citrus. However, infection increased leaf Na⁺ and Cl⁻, along with carbohydrates in roots. Pruning of roots also increased carbohydrates in intact roots, whereas shoot pruning increased carbohydrates in shoots. Carbohydrates are translocated as reducing sugars, which collectively form organic osmolytes. Because changes in concentrations of osmolytes regulate osmotic potential in plant cells, we hypothesize that increasing concentrations of organic osmolytes in an organ displaces inorganic osmolytes. We measured the osmotic potentials of young citrus trees under nematode infection, stem girdling, and root pruning at two salinity levels. All treatments reduced leaf osmotic potentials at four sampling times. At harvest, 16 days after pruning and girdling treatments, organs with higher carbohydrates had lower inorganic osmolytes and vice versa, regardless of the treatment. Pruning simulated effects of nematode infection, whereas girdling reduced the effects of nematodes. Results suggested that high organic osmolytes in roots displace inorganic osmolytes, thereby avoiding very low osmotic potentials.     

Comparative effects of salt and alkali stresses on growth, osmotic adjustment and ionic balance of an alkali-resistant halophyte Suaeda glauca (Bge.)

Effects of salt and alkali stresses on growth, osmotic adjustment and ionic balance of Suaeda glauca (Bge.), an alkali-resistant succulent halophyte, were compared. The results showed that alkali stress clearly inhibited the growth of S. glauca. Moreover, the concentrations of Na⁺ and K⁺ both increased with increasing salinity under both stresses, suggesting no competitive inhibition between absorptions of Na⁺ and K⁺. The mechanism underlying osmotic adjustment during salt stress was similar to alkali stress in shoots. The shared essential features were that organic acids, betaine and inorganic ions (dominated by Na⁺) mostly accumulated. On the other hand, the mechanisms governing ionic balance under both stresses were different. Under salt stress, S. glauca accumulated organic acids and inorganic anions to maintain the intracellular ionic equilibrium, but the anion contribution of inorganic ions was greater than that of organic acids. However, the concentrations of inorganic anions under alkali stress were significantly lower than those under salt stress of the same intensity, suggesting that alkali stress might inhibit uptake of anions, such as NO₃ ^– and H₂PO₄ ^–. Under alkali stress, organic acids were the dominant factor in maintaining ionic equilibrium. The contribution of organic acids to anions was 74.1%, while that of inorganic anions was only 25.9%. S. glauca enhanced the synthesis of organic acids, dominated by oxalic acid, to compensate for the shortage of inorganic anions.     

Utilization of exogenously supplied 14C-saccharose into primary metabolites and alkaloid production in Catharanthus roseus

Partitioning of exogenously supplied U-¹⁴C-saccharose into primary metabolic pool as sugars, amino acids, and organic acids was analyzed and simultaneous utilization for production of alkaloid by leaf, stem, and root in twigs and rooted plants of Catharanthus roseus grown in hydroponic culture medium was determined. Twigs revealed comparable distribution of total ¹⁴C label in leaf and stem. Stems contained significantly higher ¹⁴C label in sugar fraction and in alkaloids [47 kBq kg⁻¹(DM)] than leaf. In rooted plants, label in ¹⁴C in metabolic fractions in root such as ethanol-soluble, ethanol-insoluble, and chloroform-soluble fractions and in components such as sugars, amino acids, and organic acids were significantly higher than in stems and leaves. This was related with significantly higher content of ¹⁴C in alkaloids in stems and leaves. ¹⁴C contents in sugars, amino acids, and organic acids increased from leaf to stem and roots. Roots are the major accumulators of metabolites accompanied by higher biosynthetic utilization for alkaloid accumulation.     

Role of organic acids in the formation of the ionic composition in developing glycophyte leaves

The ionic composition in the leaves of some glycophyte plants (Phaseolus vulgaris L., Lycopersicon esculentum L., and Amaranthus cruentus L.) was studied during leaf development. Plants were grown in a stationary hydroponic culture; a growth medium contained equimolar concentrations of inorganic ions (NO ₃ ^? , Cl^?, SO ₄ ^2? , H₂PO ₄ ^? , K⁺, Ca²⁺, Mg²⁺, and Na⁺) equal to 5 mg-equiv./l for each ion. In the juvenile leaf, the main ions were K⁺ and water-soluble anions of organic acids represented mainly by di-and tricarboxylic acids in kidney bean and tomato and oxalic acid in amaranth. An increase in the total amount of organic anions, coinciding with the accumulation of bivalent cations, was registered in leaves of glycophytes during their development. Mature and senescing leaves of tomato and kidney bean accumulated mainly di-and tricarboxylic acid salts with the prevalence of Ca²⁺ ions. In amaranth leaves, the formation of water-insoluble (acid-soluble) oxalate pool containing Ca²⁺ ions (mature leaves) or Ca²⁺ and Mg²⁺ ions (senescing leaves) was registered. The priority role of the metabolism of organic acids in the formation of the ionic composition of glycophyte leaves during their development is discussed. It is supposed that the species-specific ionic composition of glycophyte leaves at different developmental stages is due mainly to the pattern of carbon metabolism causing the accumulation either of di-and tricarboxylic acids or oxalic acid.     

Physiological and metabolomic responses of bermudagrass (Cynodon dactylon) to alkali stress

Bermudagrass (Cynodon dactylon) is a widely used warm‐season turfgrass species with superior stress tolerance except for cold. In this study, a comparative analysis of the responses to alkali stress in bermudagrass at the physiological and metabolomic levels were performed. Mild alkali with relatively low pH slightly inhibited growth of bermudagrass as evidenced by lower electrolyte leakage, more rapid growth and higher survival rate when compared to moderate and severe alkali treatments. Moreover, the amount of 37 metabolites including amino acids, organic acids, sugars and sugar alcohols were modulated by the alkali treatments. Among them, 15 metabolites were involved in carbon and amino acid metabolic pathways. Under mild alkali stress, bermudagrass possibly slowed down metabolisms to maintain basic growth. However, moderate and severe alkali‐stressed plants accumulated significantly higher amount of carbohydrates which might result in carbon starvation. Taken together, alkali stress had severely inhibitory effect partially due to combined ionic stress and high pH stress. These results suggested that bermudagrass employed different strategies in response to alkali stresses with different pH and ionic values.