Plant Growth Regulation

Copper (Cu) in excess can disturb the cell redox status maintained by reactive oxygen- (ROS) and nitrogen species. With the help of the nitric oxide (NO)-deficient nia1nia2noa1-2 mutant, the role of NO in copper stress tolerance and its relationship with ROS was examined. Under control conditions and also during Cu exposure, the NO level in the cotyledon and root tip of the mutant was significantly lower compared to the wild-type (WT) suggesting the contribution of the nitrate reductase- and nitric oxide associated 1-dependent pathways to NO synthesis. The cell viability decrease was more pronounced in the triple mutant and the originally low growth rate was maintained under Cu stress. The endogenous NO level of the mutant was increased by NO donor addition and its cell viability significantly improved suggesting that the Cu sensitivity of the nia1nia2noa1-2 mutant is directly associated with its low NO content. As the effect of Cu increased ROS formation occurred in WT roots, while the originally high ROS levels of the triple mutant slightly decreased, still remaining significantly higher than those in the WT. In the cotyledons of the triple mutant 5 µM Cu induced ROS production but NO formation failed, while in the WT cotyledons NO but no ROS accumulation was observed. The promoting effect of NO deficiency on ROS production assumes an antagonism between these molecules during Cu stress. Based on the results, it can be concluded that NO contributes to copper tolerance and its deficiency favours for ROS production.

The aim of this research was to study the responses of two lines of Medicago ciliaris: TN11.11 and TN8.7 to iron deficiency under saline conditions. However; the paper showed also the results of a preliminary study which report the contrastive responses of the two lines to salinity. We found that plant growth and chlorophyll content of TN11.11 line were more affected by salinity than TN8.7. The severity of symptoms was linked to the sodium accumulation in shoots as well as a limitation of potassium uptake. Our data allowed us to note that TN8.7 line is less sensitive and can better cope with the salinity. Concerning the effect of salinity on iron deficiency responses, we noted that root PM H+-ATPase and FCR activities were reduced when iron deficiency was associated with salinity. This probably explained the decrease of Fe uptake. On the contrary, PEPC activity was not affected.

To explore the molecular mechanism of allelopathic rice in response to low nitrogen (N) supply or accompanying weed stress, allelopathic rice PI 312777 and its counterpart Lemont were grown under low N supply or co-cultured with barnyardgrass [Echinochloa crus-galli (L.) Beauv.] in hydroponics. The suppression subtractive hybridization (SSH) technique was employed to isolate the up-regulated genes in the treated rice accession. The results indicated that the expression of the genes associated with N utilization was significantly up-regulated in allelopathic rice PI 312777, and the higher efficiency of N uptake and its utilization were also detected in PI 312777 than that in Lemont when the two rice accessions were exposed to low N supply. This result suggested that the allelopathic rice had higher ability to adapt to low N stress than its non-allelopathic counterpart. However, a different response was observed when the allelopathic rice was exposed to accompanying weed (barnyardgrass) co-cultured in full Hoagland solution (normal N supply). It showed that the expression of the genes associated with allelochemical synthesis and its detoxification were all up-regulated in the allelopathic rice when co-cultured with the target weed under normal N supply. The results suggested that the allelopathic rice should be a better competitor in the rice-weed co-culture system, which could be attributed to increasing de novo biosynthesis and detoxification of allelochemicals in rice, consequently resulting in enhanced allelopathic effect on the target and preventing the autotoxicity in this process. These findings suggested that the accompanying weed, barnyardgrass is not only the stressful factor, but also one of the triggers in activating allelopathy in rice. This implies that the allelopathic rice is sensible of the existing target in chemical communication.

Growth rate, mineral composition and changes in polyamine concentration induced in response to salinity were studied in six crop species: spinach, lettuce, bean, pepper, beetroot and tomato. Salinity decreased growth rate, but sensitivity differed amongst the species: pepper being the most sensitive, followed by bean, tomato, lettuce and spinach, with beetroot being the most tolerant. The increase of Na+ and total cation with salinity in shoots was the highest in spinach and beetroot, the most tolerant species, while in pepper it was the lowest. Changes in putrescine (Put) concentration in shoots were related to salinity tolerance (increased in the most sensitive), while changes in spermidine (Spd; decreases) and spermine (Spm; increases) were similar with most species, except for pepper in which salinity strongly increased Put, Spd and Spm. Therefore, total polyamine concentration increased in pepper shoot, while it decreased in the other species. Thus, results show that Put accumulation was a consequence of salt stress in the most sensitive species, while salt tolerant species (beetroot) showed little change in polyamine concentration, and higher concentration in both Na+ and total cations. The role of polyamines or cation increased concentration after saline treatment in species with different salt tolerance is discussed.

Expansion in apple fruit (Malus domestica Borkh. cv. Braeburn) during early development was induced by injecting 2,4-dichlorophenoxyacetic acid (2,4-D) through the calyx of the fruit and by dipping the apples in N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU). Cell wall composition was analysed, focusing on the hemicellulose fraction containing xyloglucan, a polysaccharide believed to play an important role in cell expansion. Changes were observed in the yields of the cell wall fractions of the fruit treated with either 2,4-D or CPPU, although the monosaccharide composition of the fractions exhibited few differences. There was no decrease in the molecular weight of the xyloglucan from treated fruit. These results are discussed in terms of current cell wall expansion mechanisms.

BES1/BZR1 is a kind of transcription factors in brassinosteroid signal pathway, which play a vital role in plant growth and development, the responses to stresses in many plants, like Arabidopsis and rice. However, there are few reports for BES1 in potato, which is an important crop in China. Here, we identified nine potato BES1 genes by genome-wide analysis, and amplified all these CDS sequences which were localized on eight chromosomes. All StBES1 proteins had conserved domains including bHLH domains, BIN2 phosphorylation sites and nucleus localization sites, and shared similar motif compositions. The gene expression displayed differential in different organs and under different hormone and stress treatments. Subcellular localization showed that all StBES1 proteins localized in nucleus and cytoplasm, and transactivation assay indicated these nine StBES1 proteins played roles as transcription factors. All these results provide a theoretic basis for further studying StBES1 functions in potato.

Lotus tenuis is a perennial legume with a good adaptation to infertile, heavy and waterlogging soils. It can replace alfalfa in these sites with a similar feeding value. An important constraint is its weak competitive capacity with other graminae and weed species in permanent pastures, having consequently a poor forage yield. The objective of the present research is to overcome this disadvantage, enhancing its competitive ability with foliar applications of GA3 (GA) and phosphorus (P), increasing L. tenuis forage yield. Field experiments were conducted during 1994 with foliar application of GA (50 mg.l-1) and during 1995 with foliar application of GA (25 and 50 mg.l-1), phosphorus (8 kg.ha-1, as P2O5) and their combinations, in permanent pastures with L. tenuis and other companion grasses. In 1994 GA 50 increased significantly L. tenuis dry matter (DML) in 64.6% but not the dry matter of graminae fraction (DMG) and in consequence the total dry matter of the pasture (TDMP) was increased. In 1995 all GA treatments and their combinations with phosphorus enhanced DML but not DMG. In this sense GA 25 + P was the most effective treatment with a 151% increment of DML. Consequently TDMP was significantly increased due to a larger participation of L. tenuis in the forage yield. This increase was achieved due to a greater length and diameter of L. tenuis branches, with a logical modification in leaf:stem ratio. Moreover GA treatments reduced L. tenuis flower number. Phosphorus treatment, applied alone, showed an increase in the DML. GA treatments did not modify the feeding value of the forage in L. tenuis and graminae fractions, except GA 50 and GA 50 + P in acid detergent fiber (ADF), neutral detergent fiber (NDF) and crude protein (CP), respect to the control. The total crude protein (CP.m-2) was enhanced in all GA and GA + P treatments. Foliar GA3 and phosphorus spray applications increased the competitiveness of trefoil for light, on account of morphological changes in the spatial disposition of L. tenuis stems reaching faster the top of the pasture canopy. This practice can be an adequate alternative to increase the forage yield and total crude protein in permanent and cultivated pastures with a low cost-benefit ratio.

Meta-Topolin riboside was selected as cytokinin for these experiments. The effects of combinations of monochromatic blue, red and far red LED light were compared to fluorescent light during the micropropagation and rooting of a recalcitrant pear (Pyrus communis L.). During the micropropagation phase, red light gave some particular advantages: maximal shoot length and leaf area were obtained. Under blue light, callus weight quadrupled compared to fluorescent light. Although far red was advantageous for shoot number, shoot quality was inferior because of hyperhydricity and chlorosis as indicated by a low Chlorophyll a + b and carotenoid content. The smallest leaf area was detected under fluorescent light. Blue + red showed significant improvements. Shoot cluster weight and ‘shoot weight/callus weight’ ratio was maximal, as well as shoot number and shoot length. Leaves were also dark green, showing a maximal Chlorophyll a + b and carotenoids content. Adventitious rooting of in vitro cultured pear plants was highly affected by different light spectra and the addition of a new rooting compound: trans-cinnamic acid. Without trans-cinnamic acid, limited rooting was observed under red, blue and blue + red light. In combination with trans-cinnamic acid, 100% rooting was achieved under red light.

To detect microRNAs (miRNAs) involved in determining kernel row number in maize, next generation deep sequencing was performed on an elite inbred line Zong3 (row number 14–16) of maize in China and a single segment substitution line (SSSL) SSL-10 (row number 8–10) derived from the same genetic background. In SSL-10, the single segment is inserted in chromosome 1 between molecular marker bnlg1953 and bnlg1811. Twenty-eight miRNAs belonging to 11 conserved miRNA families in maize showed expression differences >2-fold in the two lines, among which 14 members from four miRNA families were up-regulated and 14 members from 7 miRNA families were repressed in SSL-10. A genome wide degradome was sequenced to validate the miRNA target genes in solid experiment. In addition, novel miRNAs associated with ear development were predicted using a series of strict criteria, and 29 miRNAs representing eight families were predicted as novel miRNAs. Among the novel miRNAs, only one showed an expression difference >2-fold. The conserved and novel miRNAs with >2-fold expression differences were treated as candidate miRNAs involved in maize kernel row number determination. MiRNA-dependent gene expression regulation and physiological and morphological effects on ear development may explain why the SSSL changed kernel row number compared with its recurrent parent. Based on the interaction of miRNAs and their target genes, a possible miRNA-dependent pathway leading to the given DNA fragment inducing a change in kernel row number was proposed.