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Magnesium (Mg) is essential for many biological processes in plant cells, and its deficiency causes yield reduction in crop systems. Low Mg status reportedly affects photosynthesis, sucrose partitioning and biomass allocation. However, earlier physiological responses to Mg deficiency are scarcely described. Here, we report that Mg deficiency in Arabidopsis thaliana first modified the mineral profile in mature leaves within 1 or 2 days, then affected sucrose partitioning after 4 days, and net photosynthesis and biomass production after 6 days. The short-term Mg deficiency reduced the contents of phosphorus (P), potassium, manganese, zinc and molybdenum in mature but not in expanding (young) leaves. While P content decreased in mature leaves, P transport from roots to mature leaves was not affected, indicating that Mg deficiency triggered retranslocation of the mineral nutrients from mature leaves. A global transcriptome analysis revealed that Mg deficiency triggered the expression of genes involved in defence response in young leaves.

Magnesium (Mg) is essential for many biological processes in plant cells, and its deficiency causes yield reduction in crop systems. Low Mg status reportedly affects photosynthesis, sucrose partitioning and biomass allocation. However, earlier physiological responses to Mg deficiency are scarcely described. Here, we report that Mg deficiency in Arabidopsis thaliana first modified the mineral profile in mature leaves within 1 or 2 days, then affected sucrose partitioning after 4 days, and net photosynthesis and biomass production after 6 days. The short-term Mg deficiency reduced the contents of phosphorus (P), potassium, manganese, zinc and molybdenum in mature but not in expanding (young) leaves. While P content decreased in mature leaves, P transport from roots to mature leaves was not affected, indicating that Mg deficiency triggered retranslocation of the mineral nutrients from mature leaves. A global transcriptome analysis revealed that Mg deficiency triggered the expression of genes involved in defence response in young leaves. [ABSTRACT FROM AUTHOR]

Hydroponic culture was used to comparatively investigate the copper (Cu)-induced alteration to sucrose metabolism and biomass allocation in twoElsholtzia haichowensisSun populations with one from a Cu-contaminated site (CS) and the other from a non-contaminated site (NCS). Experimental results revealed that biomass allocation preferred roots over shoots in CS population, and shoots over roots in NCS population under Cu exposure. The difference in biomass allocation was correlated with the difference in sucrose partitioning between the two populations. Cu treatment (45 μM) significantly decreased leaf sucrose content and increased root sucrose content in CS population as a result of the increased activities of leaf sucrose synthesis enzymes (sucrose phosphate synthetase and sucrose synthase) and root sucrose cleavage enzyme (vacuolar invertase), which led to increased sucrose transport from leaves to roots. In contrast, higher Cu treatment increased sucrose content in leaves and decreased sucrose content in roots in NCS population as a result of the decreased activities of root sucrose cleavage enzymes (vacuolar and cell wall invertases) that led to less sucrose transport from leaves to roots. These results provide important insights into carbon resource partitioning and biomass allocation strategies in metallophytes and are beneficial for the implementation of phytoremediation techniques. [ABSTRACT FROM PUBLISHER]

Abstract: Adequate soil calcium (Ca2+) levels are crucial for sustained reproductive development of peanut (Arachis hypogaea). A role for calcium dependent protein kinase was evaluated during peanut fruit development under sufficient and deficient soil Ca2+ conditions. Quantitative RT-PCR and protein gel blot analyses confirmed transcriptional upregulation of CDPK in seeds developing under inadequate soil Ca2+ regimen, as well as spatiotemporal regulation of CDPK expression during early mitotic growth and later during the storage phase of seed development. However, a consistent basal level of CDPK was present during similar developmental stages of pod tissue, irrespective of the soil Ca2+ status. Immunolocalization data showed CDPK decoration primarily in the outer most cell layers of the pericarp and around vascular bundles linked by lateral connections in developing pods, as well as the single vascular trace supplying nutrients to the developing seed. Finally, carbohydrate analyses and qRT-PCR data are provided for peanut genes encoding enzymes involved in sucrose cleavage (orthologs of Vicia faba, VfCWI1 and VfCWI2) and utilization (AhSuSy and AhSpS), and oleosin gene transcripts (AhOleo17.8 and AhOleo18.5) validating a role for CDPK in the establishment and maintenance of sink strength, and subsequent onset of storage product biosynthetic phase during seed maturation. [Copyright &y& Elsevier]

To unravel the roles of sucrose synthase in carrot, we reduced its activity in transgenic carrot plants by an antisense approach. For this purpose, the cDNA for the main form of carrot sucrose synthase was expressed in antisense orientation behind the 35S promoter of cauliflower mosaic virus. In independent antisense plant lines grown in soil, sucrose synthase activity was reduced in tap roots but not in leaves. In the sink organs, sucrose utilization was markedly decreased and higher levels of sucrose but lower levels of UDP-glucose, glucose, fructose, starch and cellulose were found. The phenotype of the antisense plants clearly differed from that of control plants. Both leaves and roots were markedly smaller, and the antisense line with the lowest sucrose synthase activity also developed the smallest plants. In most of the plant lines, the leaf-to-root dry weight ratios were not changed, suggesting that sucrose synthase in carrot is a major determinant of plant growth rather than of sucrose partitioning. In contrast to the acid invertases, which are critical for partitioning of assimilated carbon between source leaves and tap roots (Tang et al., Plant Cell 11: 177–189 (1999)), sucrose synthase appears to be the main sucrose-cleaving activity, feeding sucrose into metabolism. [ABSTRACT FROM AUTHOR]

Sucrose synthase, which cleaves sucrose in the presence of uridine diphosphate (UDP) into UDP-glucose and fructose, is thought to be a key determinant of sink strength of heterotrophic plant organs. To determine the roles of the enzyme in carrot, we characterized carrot sucrose synthase at the molecular level. Two genes (Susy*Dc1 and Susy*Dc2) were isolated. The deduced amino acid sequences are 87% identical. However, the sequences upstream of the translation initiation codons are markedly different, as are the expression patterns of the two genes. Susy*Dc2 was exclusively expressed in flowers. Transcripts for Susy*Dc1 were found in stems, in roots at different developmental stages, and in flower buds, flowers and maturing seeds, with the highest levels in strong utilization sinks for sucrose such as growing stems and tap root tips. Expression of Susy*Dc1 was regulated by anaerobiosis but not by sugars or acetate. The carrot sucrose synthase protein is partly membrane-associated and this insoluble form may be directly involved in cellulose biosynthesis. Tap roots of the carrot cultivar used accumulated starch in the vicinity of the vascular bundles, which correlated with high sucrose synthase transcript levels. This finding suggests that soluble sucrose synthase in tap roots channels sucrose towards starch biosynthesis. Starch accumulation appears to be transient and may be involved in sucrose partitioning to developing tap roots. [ABSTRACT FROM AUTHOR]

The steady-state levels of transcripts for cellwall β-fructofuranosidase (cwβF), for isoenzymes I and II of soluble acid β-fructofuranosidase (sI, sII), and for sucrose synthase (ss) were determined in the sink and source organs of developing carrot ( Daucus carota L.) plants. The expression patterns of the four genes clearly differed. The expression of the gene for cwβF was development-specific but not organ-specific; high transcript levels were only found in plants with primary roots, with about equal amounts in leaf lamina, petioles and roots. The genes for sI and sII were mainly expressed in roots, sI predominating in primary roots and sII in developing tap roots. Transcripts for ss were found at a low level in all developing plant organs and were markedly up-regulated during the development of young leaves and during the transition of primary roots to tap roots. Developing tap roots contained only transcripts for sII and for ss. Marked alterations in the expression of these two genes after manipulation of the source/sink balance of these plants indicates their importance in sucrose partitioning. We suggest that ss regulates sucrose utilization in developing tap roots, whereas sII located in the vacuole controls sucrose storage and sugar composition. [ABSTRACT FROM AUTHOR]

The amount of carbon transported into storage organs of crop plants to a large degree determines crop yield. The role of sucrose-cleaving enzymes in this process is not clear and it is the main goal of our work to tackle this question. Sucrose cleavage is catalysed either by invertase or sucrose synthase both of which exist in several isoforms with different subcellular locations. Carrot (Daucus carota L.) contains three major isoenzymes of acid invertase, which either accumulate as soluble polypeptides in the vacuole (isoenzymes I and II) or are ionically bound to the cell wall. Carrot sucrose synthase is thought to be a cytoplasmic enzyme encoded by two genes. cDNA clones have been isolated and characterized for cell wall invertase, for isoenzymes I and II of vacuolar invertase, and for sucrose synthase. Gene-specific fragments of these clones were used to determine the steady-state levels of transcripts in the prominent sink and source organs of developing carrot plants. The expression patterns of each gene were different and were organ- and development-specific. Developing tap roots contained only transcripts for isoenzyme II of vacuolar invertase and sucrose synthase. The source/sink balance of these plants was manipulated and only the expression of these two genes was markedly altered, indicating their importance in sucrose partitioning. Based on these results, a model is proposed for sucrose partitioning in carrot plants with developing tap roots in which sucrose synthase regulates sucrose utilization, whereas isoenzyme II of vacuolar invertase controls sucrose storage and sugar composition. [ABSTRACT FROM AUTHOR]