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Roots absorb water and nutrients from the soil, give mechanical support to plants, and supply hormones that affect many physiological and biochemical processes. Roots also exert control over whole-plant growth and development by synthesizing plant hormones and controlling the uptake of mineral nutrients. Coronatine (COR) is an analogue of jasmonic acid and is a chlorosis-inducing non-hostspecific phytotoxin with an alleviative effect on plant growth under stress conditions. A 2-year field study was conducted to determine the effect of COR on the physiological and biochemical attributes of the root and the seed yield of soybean (Glycine maxL. Cv. Zhonghuang 13). COR was foliar-applied at 10 nM during the 7-trifoliolate leafs stage. Root dry weight was significantly increased on average by 37% with COR over the 2 years. The root nitrogen concentration increased by 19.2%, phosphorus concentration by 23.3%, and potassium concentration by 31.2% following COR application. The content of cytokinins was increased by 31.5% and 46.0%, while that of abscisic acid was decreased by 45.0% and 25.5% with COR over the 2 years. Seed yield was increased 7.0% in 2008 and 9.6% in 2009, respectively, due to COR application. [ABSTRACT FROM PUBLISHER]

The effects of nitrogen (N) forms (ammonium- or nitrate-N) on plant growth under salinity stress [150 mmol sodium chloride (NaCl)] were studied in hydroponically cultured cotton. Net fluxes of sodium (Na+), ammonium (NH4+), and nitrate (NO3−) were also determined using the Non-Invasive Micro-Test Technology. Plant growth was impaired under salinity stress, but nitrate-fed plants were less sensitive to salinity than ammonium-fed plants due mainly to superior root growth by the nitrate-fed plants. The root length, root surface area, root volume, and root viability of seedlings treated with NO3-N were greater than those treated with NH4-N with or without salinity stress. Under salinity stress, the Na+content of seedlings treated with NO3-N was lower than that in seedlings treated with NH4-N owing to higher root Na+efflux. A lower net NO3−efflux was observed in roots of nitrate-fed plants relative to the net NH4+efflux from roots of ammonium-fed plants. This resulted in much more nitrogen accumulation in different tissues, especially in leaves, thereby enhancing photosynthesis in nitrate-fed plants under salinity stress. Nitrate-N is superior to ammonium-N based on nitrogen uptake and cotton growth under salinity stress. [ABSTRACT FROM PUBLISHER]

The aim of this study was to investigate the effect of silicon (Si) on soybean seedlings under (combined) drought and ultraviolet-B (UV-B) radiation stresses. Specifically, we determined dry matter accumulation and partitioning of the mineral elements in different organs of soybean seedlings using the inductively coupled plasma mass spectrometry (ICP-MS). The amount of dry matter accumulated in root, stem, and leaf of seedlings treated with (combined) drought and UV-B radiation stresses were lower than that of the control. Also, the content of macroelements in seedlings under the combined stress was lower than in those under control conditions. Changes in the contents of microelements varied according to the intensity of drought, UV-B radiation, and the organs of soybean. The relationship between the contents of mineral elements and the accumulation of dry matter also varied similarly. These results demonstrated that drought and UV-B radiation induced an alteration in the distribution of mineral elements in root, stem and leaf, leading to decreases in dry matter accumulation and inhibition of soybean growth. [ABSTRACT FROM PUBLISHER]

The aim of this study was to investigate the potential of silicon (Si) for alleviating Ultraviolet-B (UV-B) radiation stress based on changes in biomass, physiological attributes and photosynthetic characteristics of two soybean (Glycine maxL.) cultivars, Kenjiandou 43 (‘K 43’) and Zhonghuang 35 (‘ZH 35’). The cultivars were raised with and without Si in the greenhouse, and then subjected to ambient, ambient + 2.7 kJ m−2d−1and ambient + 5.4 kJ m−2d−1of UV-B radiation. Depending on cultivar, plants suffered severe growth limitations under UV-B radiation, but the application of Si alleviated the adverse effects on growth and development by increasing the stem length, net photosynthetic rate (PN) and leaf chlorophyll content. Concurrently, it decreased the stomatal conductance (Sc) and intercellular carbon dioxide (CO2) concentration (Ci). In response to the UV-B radiation stress, the antioxidant enzyme activities of superoxide dismutase (SOD) increased by 41.2–72.7%, peroxidases (POD) by 49.5–85.7%, malodialdehyde (MDA) by 6.7–20.4% and soluble protein by 4.2–7.6%. The overall results indicated that media treatment with Si might improve soybean growth under elevated UV-B radiation through positive changes in biomass and some physiological attributes that were dependent on cultivar. [ABSTRACT FROM PUBLISHER]

Genotypic differences in potassium (K) uptake and utilization were compared for eight cotton cultivars in growth chamber and field experiments. Four of the cultivars ('SGK3', 'SCRC18', 'SCRC21' and 'SCRC22') typically produce lower dry mass and the other four ('Nannong8', 'Xiangza2', 'Xinluzao12' and 'Xiangza3') produce greater dry mass in K-deficient solution (0.02 mM). The mean dry weight of seedlings (five-leaf stage) of cultivars with greater biomass was 155% higher than that of cultivars with lower biomass yield under K deficiency. However, all the genotypes had similar dry matter yields in K-sufficient solution (2.5 mM). Thus, the four cultivars with superior biomass yield under low K medium may be described as K efficient cultivars while the inferior cultivars may be described as K inefficient. Although seeds of the studied cultivars originated from different research institutes or seed companies, there were little differences in seed K content among them, irrespective of their K efficiency. Consequently, there were no significant differences in K accumulation in seedlings (4 d after germination in a K-free sand medium) just before transferring to nutrient solutions. However, the K efficient genotypes, on average, accumulated twice as much K at 21 d after transferring to K-deficient solution (0.02 mM). A much larger root system as well as a slightly higher uptake rate (K uptake per unit of root dry weight) may have contributed to the higher net K uptake by the K efficient cultivars. In addition, the K efficiency ratio (dry mass produced per unit of K accumulated) and K utilization efficiency (dry mass produced per unit of K concentration) of the K efficient cultivars exceeded those of the K inefficient genotypes by 29% and 234%, respectively, under K deficiency. On average, the K efficient cultivars produced 59% more potential economic yield (dry weight of all reproductive organs) under field conditions even with available soil K at obviously deficient level (60 mg kg-1). We noted especially that the four K inefficient cultivars studied were all transgenic insect-resistant cotton, suggesting that the introduction of foreign genes (Bt and CpTI) may affect the K use efficiency of cotton. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine if treatment with silicon (Si) may improve nutrient uptake by soybean under ultraviolet-B (UV-B) radiation stress. Soybean (Glycine max L.) cultivars, 'Kennong 18' (K 18) and 'Zhonghuang 13' (ZH 13), were grown in hydroponic cultures under ambient and supplemental levels of ultraviolet-B (UV-B, 280-315 nm) with and without Si. Supplemental UV-B radiation simulating 30% stratospheric ozone depletion significantly decreased plant biomass by 74.9 to 135.6%, increased leaf nitrogen (N) and phosphorus (P) by 9% and 16%, respectively, decreased leaf magnesium (Mg) contents by 9%, and calcium (Ca) by 24%. UV-B radiation caused a substantial increase in the allocation of P, potassium (K) and Ca to roots compared with stem and leaves, presumably to ensure sustained nutrient uptake under the stress. Silicon application improved the uptake of P and Mg by 11%, which favored the partitioning of dry mass to shoots under UV-B radiation and the allocation of tissue P and Ca to roots. The overall changes due to Si supported a reasonable increase in dry mass of the 'K 18' cultivar. [ABSTRACT FROM AUTHOR]

Bacillus thuringensis (Bt) transgenic (insect-resistant) cotton cultivars senesce prematurely under potassium (K+) deficiency, more often than conventional cultivars, in the North China Plain. To verify if Bt-transgenic cotton was more susceptible to K+ deficit, two transgenic cultivars, 'CCRI 41' and 'DP 99B', and two conventional cultivars, 'CCRI 35' and 'CCRI 36', selected from widely used cultivars in China, were used in a seedling hydroponic study. The culture solution K+ concentration was 0.5 mM for high K+ and 0.02 mM for low K+ conditions. Seedlings of all four cultivars accumulated more dry matter and K+ when grown at high K+ than low K+ conditions. However, under low K+ condition, the dry weight and K+ content of Bt-transgenic cultivars CCRI 41 and DP 99B were lower than those of the conventional cultivars CCRI 36 and CCRI 35. The results indicated that Bt-transgenic cultivars CCRI 41 and DP 99B were more sensitive to K+ deficiency than conventional cultivars CCRI 36 and CCRI 35, which could be the reason for premature senescence symptoms observed from fields of Bt-transgenic cotton under K+ deficiency. Seedlings of all four cultivars had a higher K+ use efficiency (KUE) under low K+ than high K+ conditions, but the KUE did not account for the differential responses between Bt-transgenic and conventional cultivars at the low K+ concentration. The K+ depletion results did not reveal the mechanism for the above differential responses in Vmax and Km of the seedlings either. Further experiments with more cultivars are needed to clarify the differential mechanisms in these genotypes. [ABSTRACT FROM AUTHOR]

Conserving irrigation water resources is a most important measure for sustainable wheat production in the North China Plain. In the present study, the effect of phosphorus (P) application for saving irrigation water was evaluated. The application of fertilizer P increased nitrogen and phosphorus uptake, shoot biomass, head number, seed number and, consequently, grain yield, and increased soil water use and seasonal evapo-transpiration. The lower the volume of irrigation water applied, the more obvious were these effects. When winter wheat was basally fertilized with 88.5 kg P 2 O 5 /ha and irrigated with 90 mm at the jointing stage, the highest fertilizer P use efficiency, apparent P recovery and net profit (due to irrigation and/or fertilizer P) were obtained. The results suggested that fertilizer P should be used for saving irrigation water resources in the North China Plain. [ABSTRACT FROM AUTHOR]