Differential effect of short-term cold stress on growth, anatomy, and hormone levels in cold-sensitive versus -resistant cultivars of Digitaria eriantha

Two cultivars of Digitaria eriantha (cold-sensitive cv. Sudafricana and cold-resistant cv. Mejorada INTA) were exposed to cold stress (5?°C) for 0, 6, 24, or 72?h, and compared in terms of leaf and root growth, recovery period, shoot and leaf anatomy, and levels of chlorophyll, auxin (indole-3-acetic acid, IAA) and cytokinins (CKs). In Sudafricana, cold treatment caused reduced growth, slight changes in chlorophyll level, reduced levels of IAA and CK iso-pentenyladenine (iP), and reduced leaf dry weight (DW) and fresh weight (FW) during the recovery period. Anatomical damage was observed in chloroplasts, main stem, and axillary buds. Ultrastructural study showed reduced numbers of starch grains in chloroplasts of the bundle sheath and mesophyll. In Mejorada, cold treatment had no significant effect on growth or chlorophyll level. Leaf DW and FW quickly returned to normal levels during the recovery period. Anatomy of ground meristem was affected, but ultrastructure of bundle sheath and mesophyll chloroplasts was not. The cold tolerance of cv. Mejorada appears to be related to the stability of chlorophyll and CK levels, increase of IAA, and maintenance of normal shoot and leaf anatomy and ultrastructure.     

Field nursery inoculation of Hevea brasiliensis Muell. Arg. seedling rootstock with vesicular-arbuscular mycorrhizal (VAM) fungi

The growth response of Hevea brasiliensis to vesicular-arbuscular mycorrhizal (VAM) fungi inoculation was assessed in two field nursery sites containing indigenous mycorrhizal fungi (IMF). Seedling rootstocks were inoculated with mixed VAM-fungal species in a factorial combination with phosphorus (P) fertilizer application, and planted in randomised blocks on sandy (site 1) and clayey (site 2) soils. Plants were harvested after 26 weeks for measurements of shoot dry weight (DW), stem diameter, height, mycorrhizal root colonization and leaf nutrient contents. At site 1, VAM increased shoot DW, stem diameter and plant height only in treatments without P applied. Increases in shoot DW due to VAM were 70% greater than the uninoculated controls although this was reduced to 5% when P was applied. At site 2, VAM inoculation also increased shoot DW and stem diameter but the magnitude of the increases was smaller. Shoot DW response due to VAM was only 29%. At this second site, applying phosphate to uninoculated plants did not increase shoot yields further. Leaf concentrations of all nutrients were unaffected by VAM at both sites, except for copper (Cu) which was increased by VAM in treatments where P was not applied. However, leaf contents of P, potassium (K), magnesium (Mg) and Cu were increased by VAM at site 1, and of leaf nitrogen (N) and K at site 2. These experiments demonstrate that VAM-fungi could be introduced into field nursery sites to improve growth and P uptake by H. brasiliensis. The relevance of VAM-fungi to H. brasiliensis seedling rootstock development and the influence of IMF in determining field responses is discussed.     

Salt tolerance in Aster tripolium L. II. Ionic regulation

Abstract Measurements of tissue ion contents (Na, K and Cl) were carried out at frequent intervals on plants of Aster tripolium L. grown at a range of salinities for 36 d. Aster tripolium behaved as a typical halophyte showing high levels of inorganic ion accumulation even at low salinities. As salinity increased Na replaced K to a large extent in the shoot but root K was unaffected up to 500 mol m^?3 external NaCl. Shoot (Na + K) concentration on a tissue water basis was maintained constant in all treatments throughout the experiment, whereas shoot (Na + K) on a dry weight basis showed marked fluctuations in some treatments. An increase in (Na + K) per gram dry weight was, however, accompanied by a parallel increase in fresh weight: dry weight (FW : DW) ratio. Transport of (Na + K) to the shoot per unit root weight changed during the experiment in the manner expected, given the observed changes in shoot relative growth rate and FW : DW to result in a constant shoot (Na + K) concentration on a water basis. Chloride was the major balancing anion in the shoot at high salinity, but never accounted for more than 38% of the (Na + K) found in the root tissue. At all salinities (Na + K) salts accounted for the majority of the measured shoot sap osmotic potential. The interactions between salinity, growth, ion transport and osmotic adjustment are discussed.     

Changes in growth and photosynthetic characteristics of Ocimum sanctum under growth regulator treatments

A field experiment was conducted to investigate the effect of growth regulators on growth characteristics such as root length, shoot length, total leaf area, number of inflorescence per plant, number of flower per inflorescence, whole plant fresh weight and whole plant dry weight. Photosynthetic characteristics were also analyzed based on the same experiment. For this, various photosynthetic pigment contents such as chlorophyll, carotenoid, anthocyanin and xanthophyll content were calculated. The conventional growth regulator abscisic acid (ABA) and non-conventional growth regulator triazole compound paclobutrazol (PBZ) were used. Root length increased due to growth regulator treatment, but shoot length decreased. Leaf area was decreased due to growth regulator treatment. The number of inflorescence increased in ABA treated plants, but it was decreased in PBZ treated plants. In ABA treated plants, the number of flowers per inflorescence was increased. In PBZ treated plants the number of inflorescence was reduced. The whole plant fresh weight (FW) and dry weight (DW) were increased in ABA and PBZ treated plants. There was an increase in chlorophyll content in growth regulator treated plants compared to control, and it was more in PBZ treated plants. The carotenoid content was also increased in ABA and PBZ treated plants.     

Changes in growth and photosynthetic characteristics of Ocimum sanctum under growth regulator treatments

A field experiment was conducted to investigate the effect of growth regulators on growth characteristics such as root length,shoot length,total leaf area,number of inflorescence per plant,number of flower per inflorescence,whole plant fresh weight and whole plant dry weight.Photosynthetic characteristics were also analyzed based on the same experiment.For this,various photosynthetic pigment contents such as chlorophyll,carotenoid,anthocyanin and xanthophyll content were calculated.The conventional growth regulator abscisic acid (ABA) and non-conventional growth regulator triazole compound paclobutrazol (PBZ) were used.Root length increased due to growth regulator treatment,but shoot length decreased.Leaf area was decreased due to growth regulator treatment.The number of inflorescence increased in ABA treated plants,but it was decreased in PBZ treated plants.In ABA treated plants,the number of flowers per inflorescence was increased.In PBZ treated plants the number of inflorescence was reduced.The whole plant fresh weight (FW) and dry weight (DW) were increased in ABA and PBZ treated plants.There was an increase in chlorophyll content in growth regulator treated plants compared to control,and it was more in PBZ treated plants.The carotenoid content was also increased in ABA and PBZ treated plants.     

Foliar sprays with ABA promote growth of Ilex paraguariensis by alleviating diurnal water stress

Stomatal closure, relative water content (RWC) and vegetative growth were monitored in Ilex paraguariensis plants grown under well-watered conditions with a photosynthetic photon flux density (PPFD) varying from 100% to 1.5%, and sprayed weekly with either distilled water (control) or 1.89 mM abscisic acid (ABA). ABA treatments caused stomatal closure, ranging from 62% to 73%. These treatments also increased RWC in the early evening from 82% to 92% and 88% to 94% in mature and immature leaves, respectively. Such alleviation of the water stress was correlated with increases in leaf area, leaf dry weight (DW), shoot length and shoot DW. On day 35 from the beginning of the experiment, the increases in DW of both leaves and shoots were 1.5-fold at the 1.5% PPFD and 3-fold (for leaves) and 4.5-fold (for shoots) under 100% PPFD. In water-sprayed control plants grown under 1.5% PPFD shoot length also increased significantly, although these shoots contained more ABA (assessed by capillary gas chromatography–mass spectrometry) than those of plants grown under 100% PPFD. These results show that ABA sprayed on to leaves promotes growth in I. paraguariensis plants by alleviating diurnal water stress.     

Effect of l-arginine,casein hydrolysate,banana powder and sucrose on growth and solasodine production in shoot cultures of Solanum laciniatum

The addition of l-arginine, casein hydrolysate, banana powder and the reduction of the concentration of sucrose in the media could increase the solasodine content in the shoot cultures of Solanum laciniatum. No linear correlations between growth index, chlorophyll content and solasodine content were observed, however a positive linear correlation between solasodine productivity and chlorophyll content occurred in these shoot cultures.Abbreviations Ch chlorophyll content - DW dry weight - fl flask - FW fresh weight - GI growth index - LOD limit of detection - LOQ limit of quantitation - SDc solasodine content - SDp solasodine productivity - w week     

The effect of root pressurization on water relations, shoot growth, and leaf gas exchange of peach (Prunus persica) trees on rootstocks with differing growth potential and hydraulic conductance

It is well known that rootstocks can have an effect on the vegetative growth and development of the tree; however, there has been no clear explanation about the physiological mechanism involved in this phenomenon. Evidence indicates that the rootstock effects on tree vegetative growth may be related to hydraulic limitations of the rootstock. The objective of these experiments was to investigate the shoot growth, water potential, and gas exchange of peach trees on different rootstocks in response to manipulations of water relations of trees on rootstocks that differ in root hydraulic conductance. Tree water relations were manipulated by applying different amounts of pneumatic pressure on the root system and then relative shoot extension growth rate, tree transpiration rate, leaf water potential, leaf conductance, leaf transpiration, and net CO(2) exchange rate responses were measured. Root pressurization increased leaf water potential, relative shoot extension growth rate, leaf conductance, leaf transpiration, and net CO(2) exchange rates of trees on both vigorous and dwarfing rootstocks. There was a significant positive linear correlation between applied pneumatic pressure and tree transpiration rate and leaf water potential. Leaf conductance, transpiration rate, and net CO(2) exchange rate as well as relative shoot extension growth rates were also positively correlated with the applied pneumatic pressure on the root system. These relationships were consistent across both vigorous and size-controlling rootstocks, indicating that rootstock hydraulic limitation may be directly involved in the vegetative growth control of peach trees.     

Biomass production of Cymbopogon citratus (D.C.) stapf., a medicinal plant, in temporary immersion systems

Summary In vitro plants of lemon grass were established, starting from shoot apices derived from plants cultivated under field conditions. The effect of the immersion frequency (two, four, and six immersions per day) on the production of biomass in temporary immersion systems (TIS) of 1 liter capacity was studied. The highest multiplication coefficient (12.3) was obtained when six immersions per day were used. The maximum values of fresh weight (FW; 62.2 and 66.2 g) were obtained with a frequency of four and six immersions per day, respectively. However, the values for dry weight (DW; 6.4g) and height (8.97cm) were greater in the treatment with four immersions per day. The TIS used in this work for the production of lemon grass biomass may offer the possibility of manipulating the culture parameters, which can influence the production of biomass and the accumulation of secondary metabolites. We describe for the first time the in vitro production of Cymbopogon citratus biomass in TIS.     

Root to shoot communication and abscisic acid in calreticulin (CR) gene expression and salt-stress tolerance in grafted diploid potato clones

Potato is an important world crop but its cultivation is relatively limited by its sensitivity to salt-stress. Auto- and hetero-grafting was used to examine the effect of rootstock and abscisic acid (ABA) on expression of the Ca²⁺-storage protein calreticulin (CR) and salt-stress tolerance in potato. Sibling-selected diploid clones of potato (S. tuberosum) were utilized that are distinguished by differential root Na⁺ absorption; including type: late-maturing, LM and excluding type, early-maturing, EM under salt treatment; salt-stress sensitivity (S/T, sensitive or tolerant); and abscisic acid production (AD/AN, ABA-deficient or-normal sibling lines). CR expression, osmotic potential (OP) and leaf Ca²⁺ were measured at the end of a 5 days NaCl stress treatment applied at tuber initiation. Increased CR expression was induced by NaCl stress and associated with salt tolerance in early-maturing tolerant (EMT) and late-maturing tolerant (LMT) clones with higher levels of CR in LMT compared to the EMT clone. Early-maturing sensitive (EMS) clone salt tolerance increased when grafted onto LMT but not onto EMT rootstocks. EMS scions maintained less negative leaf OP when grafted onto LMT rootstocks than grafting onto the EMT rootstock. Exogenous ABA application induced a less negative upper leaf OP in the salt-stress sensitive AD clone but not in the AN clone. AD clones were characterized by low CR levels, which did not increase after stress. However, grafting the AD clone onto LMT increased CR expression in the AD portion of the graft combination. Salt-stress induced CR expression and is positively associated with the presence of ABA and the salt-stress tolerant phenotypes. Both, elevation in CR expression and salt tolerance in the tolerant rootstocks, were translocated to sensitive scions although highest permeation depended on the LM type. Calreticulin expression appears to be involved in ABA-induced salt tolerance and both salt-stress tolerance and CR expression appear to be regulated by the roots.     

滇中喀斯特41种不同生长型植物叶性状研究

该研究以云南石林喀斯特地区41种主要植物(乔木19种、灌木10种、藤本4种、草本8种)为对象,对其叶面积(AR)、叶鲜重(FW)、叶干重(DW)、叶厚度(TH)、叶绿素含量(Chlc)等进行了测定,得到不同植物比叶面积(SLA)、叶干物质含量(DMC)等指标。结果表明:(1)在物种水平上7项植物叶性状值变化范围较大,不同生长型植物差异显著。(2) 41种植物的SLA与DMC之间呈极显著负相关(P0.01),AR与FW、DW呈极显著正相关(P0.01),TH与Chlc呈极显著正相关(P0.01),其他因子间相关性不显著。(3)该研究区植物叶性状变异范围为15.82%～139.14%,多为高变异系数(84.40%～131.01%),叶性状变异中AR与FW贡献率较高,分别为84.40%、90.28%,不同生长型植物在TH上稳定性较好。(4)石林喀斯特地区植物叶片适应特殊生境时表现出较低的TH、SLA、Chlc和较高的DMC等特征。这说明石林喀斯特地区植物通过形成不同的叶性状特征来适应特殊生境,可为喀斯特地区的植被保护与恢复提供理论指导。     

海滨沙地单叶蔓荆匍匐茎对沙埋适应的生长对策

单叶蔓荆(Vitex trifolia var.simplicifoli)是一种耐盐、耐旱固沙地被植物。依据海滨沙地自然沙埋特点对单叶蔓荆匍匐茎进行了不同厚度(半埋和全埋)和不同长度交叉沙埋处理,研究探讨了单叶蔓荆沙埋适应生长对策,为其开发利用、科学管理和海滨环境修复提供指导。结果表明,正常情况下,单叶蔓荆匍匐茎基部和中部生长缓慢,顶部生长快。轻度(沙埋匍匐茎基部)和中度(沙埋匍匐茎基部和中部)半埋和全埋使匍匐茎顶部生长加速,茎长增长量较对照高出1.5到3.1倍;但重度(沙埋整个匍匐茎)半埋和全埋使匍匐茎顶部净增长量减少12%和13%。在20d沙埋中,对照整个匍匐茎各段均无不定根长出,但不同程度半埋和全埋沙埋处理下沙下匍匐茎上均长出不定根,重度半埋使不定根生长受抑;同时匍匐茎上各段茎生物量上升,枝叶生物量下降,且随着沙埋程度的增加而增减幅度提高,在重度半埋和全埋达到最大。在轻度和中度半埋和全埋下,匍匐茎上未沙埋部位枝条生长加速。研究表明,在自然环境中,单叶蔓荆匍匐茎顶端是一个对环境变化反应敏感的部位,并与沙埋后单叶蔓荆茎延伸生长和植株能否生存密切相关。当匍匐茎顶部没被沙埋时,沙埋促进沙埋部位匍匐茎和枝叶中物质转移,加速匍匐茎顶部快速生长和物质积累以弥补沙埋带来的损伤维持物质和能量的代谢平衡。沙埋后,单叶蔓荆以茎顶端快速生长、形成不定根、枝条生长维持茎水分平衡和能量和物质代谢平衡,以快速生长摆脱沙埋影响的生长方式为其对沙埋环境的重要适应对策。因此,在海岸沙地单叶蔓荆种群管理和维护中,在强风移沙引起的重度沙埋后,及时剥离匍匐茎顶部沙子对维护单叶蔓荆种群的延续生存和扩散均有重要作用。     

Water relations and growth of rose plants cultured in vitro under various relative humidities

Stomatal malfunctioning is one of the main reasons why plants desiccate when transferred from in vitro to greenhouse conditions. In order to overcome this problem in Rosa hybrida cv. Madame G. Delbard (R) Deladel, two techniques, bottom cooling and water vapour permeable lid, were used. Both methods aimed to increase the vapour pressure gradient between leaf and atmosphere and consequently to improve plant transpiration.The results showed that these techniques increased leaf resistance to dehydration and improved stomatal regulation. Water relations of treated plantlets were similar to those generally observed in hardened plants: lower leaf water and osmotic potentials, and lower leaf water content than in the control ones. Osmotic adjustment occurred in treated plantlets maintaining turgor pressure. Each technique also induced some effects on growth during the rooting phase: with bottom cooling, roots were shorter, with permeable lids, apices were necrosed.These results are discussed in terms of physiological causes and in terms of effect during the following acclimatization.Abbreviations AWC absolute water content - DW dry weight - FW fresh weight     

Shoot growth and distribution pattern ofCarex kobomugi in a natural stand

To clarify the growth and distribution ofCarex kobomugi, I surveyed the shoot heights and weights of a population growing in a sand dune at Sindu-ri, Wonbuk-myeon, Taean-gun, in Chungnam Province, Korea. During the growing season, size classes, based on leaf number and shoot heights, shifted, with those in the medium class moving to higher classes. Although the frequencies of those class characters showed a normal distribution curve throughout the season, the frequencies of each class based on shoot weight were evenly distributed in all size classifications. Coefficients of variation were 0.17 for leaf number, and 0.35 for leaf length and weight per plant. The maximum numbers of leaves were 8.16 ± 1.38 per plant for those that were non-flowering, but 2.66 ± 0.62 per plant for those that did flower. Non-flowering plants exhibited withered leaves by mid-September, while withering began in male plants by mid-May and by mid-July for females. At the end of the growing season, the lengths and weights of leaves from non-flowering plants were 47.8 ± 16.6 cm and 1773 ± 628 mg, respectively. When leaf order was considered, leaves increased in size along two-thirds of the ranking, then decreased. In a separate analysis, the growth ofCarex plants was compared with those ofElymus mollis in the same sample quadrats. Biomass of the former accounted for only a small portion of the total biomass per unit area (E. mollis having a dry weight of >76.4 g m^-2), but under such competition, the leaf lengths and individual plant weights nonetheless increased forCarex as well.     

Leaf traits indicate survival strategies among 42 dominant plant species in a dry, sandy habitat, China

The objective of this paper was to assess the congruency of leaf traits and soil characteristics and to analyze the survival strategies of different plant functional types in response to drought and nutrient-poor environments in the southeastern Ke’erqin Sandy Lands in China. Six leaf traits-leaf thickness (TH), density (DN), specific leaf area (SLA), leaf dry weight to fresh weight ratio (DW/FW), leaf N concentration (N_mass), and N resorption efficiency (NRE_mass)-of 42 plant species were investigated at four sites. The correlations between leaf traits and soil characteristics-organic C (OC), total N (TN), total P (TP), and soil moisture (SM)-were examined. We found that the six leaf traits across all the 42 species showed large variations and that DW/FW was negatively correlated with OC, TN, TP, and SM (P<0.05), while other leaf traits showed no significant correlations with soil characteristics. To find the dissimilarity to accommodate environment, a hierarchical agglomerative clustering analysis was made of all the species. All the species clustered into three groups except the Scutellaria baicalensis. Species of group III might be most tolerant of an arid environment, and species of group II might avoid nutrient stress in the nutrient-poor environment, while group I was somewhat intermediate. Therefore, species from the different groups may be selected for use in vegetation restoration of different sites based on soil moisture and nutrient conditions.     

Survival and growth of konara oak (Quercus serrata Thunb.) seedlings in an abandoned coppice forest

Survival and growth of konara oak (Quercus serrata) seedlings were examined on the forest floor of a konara oak coppice stand in Mitaka, Tokyo, for 5 yr (1976–1980) after exclusion of human management. Attention was mainly focused on a large cohort derived from a bumper acorn crop in 1975. Seedlings began to branch in the second year, although some did not branch during the whole 5-yr period. Branched seedling showed higher survival and greater weight in 1980 than unbranched seedlings. Many of the branched seedlings had lost an orthotropic leader shoot and spread their branches laterally, suggesting a response for efficient light-capture. As for unbranched seedlings, a size relationship between leaf area and stem length developing every year was dependent on the shoot size. A small shoot gave priority to enlargement of leaf area, whereas a large shoot gave priority to stem elongation. Yearly variations in seedling mortality and stem elongation were related to the amount of precipitation. Both the initial height and leaf area of germinated seedlings were positively correlated with their survival and weight after five years. Five-year survival of seedlings showed a positive correlation with light intensity at the growth site but a negative correlation with the extent of leaf predation. Sprouts of shrub species grew vigorously and became much taller than the oak seedlings in the 5-yr observation period. The characteristics of forest-floor seedlings were discussed in relation to the regeneration of konara oak forests in general.     

The sediment burial depth and salinity control the early developments of Suaeda salsa in the Yellow River Delta

Sediment deposition is a common phenomenon in the estuary area. Pot control experiments were conducted to evaluate the interaction effects of sediment burial depth and salt stress on the seed germination and early seedling growth of Suaeda salsa (L.) Pall., an pioneer species of tidal wetland near the Yellow River Delta. The results showed that the percentage of seedling emergence, seedling emergence rate, seedling height, branch number, shoot biomass and root biomass were all significantly affected by salt stress and sediment burial depth. While the interaction of salt and burial depth significantly influenced the branch number, leaf biomass, shoot biomass and total plant biomass. Only 5 cm burial depth without salt stress should 6.25 ± 3.61% seedlings emergence. With the increasing of sediment burial depth and salt stress, percentage of seedling emergence, seedling emergence rate and plant height decreased significantly. However, under the salt treatment of 0 and 1%, the branch number increased dramatically with the increasing of sediment burial depth from 0 to 3 cm. The ratio of leaf to total biomass increased with increasing of burial depth, on the contrary, the ratio of root to total biomass decreased. 0–1 cm sediment burial depth was proved the suitable depths for seed germination of S. salsa in the coastal wetland of the Yellow River Delta. Our findings contribute to a better understanding of how to improve the seedling establishment of S. salsa under the dynamic changes of sediment deposition and salinity in the coastal wetland of the Yellow River Delta.     

Carbon and nitrogen economy of 24 wild species differing in relative growth rate

The relation between interspecific variation in relative growth rate and carbon and nitrogen economy was investigated. Twentyfour wild species were grown in a growth chamber with a nonlimiting nutrient supply and growth, whole plant photosynthesis, shoot respiration, and root respiration were determined. No correlation was found between the relative growth rate of these species and their rate of photosynthesis expressed on a leaf area basis. There was a positive correlation, however, with the rate of photosynthesis expressed per unit leaf dry weight. Also the rates of shoot and root respiration per unit dry weight correlated positively with relative growth rate. Due to a higher ratio between leaf area and plant weight (leaf area ratio) fast growing species were able to fix relatively more carbon per unit plant weight and used proportionally less of the total amount of assimilates in respiration. Fast growing species had a higher total organic nitrogen concentration per unit plant weight, allocated more nitrogen to the leaves and had a higher photosynthetic nitrogen-use efficiency, i.e. a higher rate of photosynthesis per unit organic nitrogen in the leaves. Consequently, their nitrogen productivity, the growth rate per unit organic nitrogen in the plant and per day, was higher compared with that of slow growing species.     

Ascorbic acid improves the tolerance of wheat plants to lead toxicity

Among the heavy metals (HMs), lead (Pb) is considered as a toxic HM which adversely affects growth and development of crop plants. The present experiment was aimed to investigate the potential role of ascorbic acid (ASC) in the reversal of Pb-inhibited nitrogen and sulfur assimilation enzymes activity and activity of photosynthesis enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and growth response in wheat plants. Wheat seedlings were subjected to 0 mM (control) and 0.2 mM and 0.6 mM of ASC with and without 2 mM of Pb. Plants treated with Pb exhibited the following reduced growth characteristics (root length, shoot length, root fresh weight (FW), shoot FW, root dry weight (DW) and shoot DW). A decrease was also observed in the activity of Rubisco and ATP sulfurylase (ATP-S), relative water content (RWC), accumulation of total chlorophyll (Total Chl) and content of nutrients [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg)] in Pb-treated plants. However, an increase in Chl degradation and in the activity of O-acetylserine(thiol)lyase (OAS-TL) and accumulation of cysteine (Cys), malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) was observed in plants under Pb stress. On the contrary, exogenous application of ASC mitigated the Pb-toxicity-induced oxidative damage by enhancing the activities of antioxidant enzymes, such as superoxide dismutase, catalase and glutathione reductase. Improved activity of antioxidant enzymes suppressed the formation of MDA and H₂O₂, which was reflected in the form of improved growth characteristics. Moreover, ASC induced improvement in plants defense systems by reduced Chl degradation and improved the content of essential nutrients (N, P, K, Ca and Mg) and Cys, RWC and the activity of Rubisco, ATP-S, NR and OAS-TL.     

Actinidia deliciosa C.F. Liang in vitro

In vitro growth of Actinidia deliciosa C.F. Liang, cv Hayward and changes in mineral composition of the medium and in the different parts of the explants (callus, stem and leaves), were analyzed after 0, 15, 30, 45 and 60 days of culturing in each of three successive 60 days subcultures.Fresh (FW) and dry weight (DW) of the explants increased mainly during the first 30 days of culturing, with a predominant increase of FW in leaves and an equal distribution in DW in callus and leaves. Stem FW and DW changes were lower than those observed with callus and leaves. As FW and DW of the explants increased the FW and DW of the medium decreased.The presence of the explants induced a large decrease of medium pH during the first 15 days of culturing followed by a return to the initial level at the end of the culturing.The initial P content of the MS medium was insufficient for the long term culturing, as after 30 days of culturing almost all (94.5%) the P present in the medium was absorbed by the explants and evenly distributed in their different parts. During the first month, 85% of the initial N was absorbed. At the end of the culture only 2% of the initial P and 5% of N remained in the medium. These two elements were equally distributed in callus and leaves during the first month of culturing, while in the last 30 days they increased only in the callus.MS medium initial concentrations of K, Mg, Ca, Fe, Zn, Mn and Cu were sufficient for 60 days explants growth. Almost all these elements were absorbed during the first 30 days of culturing. Their distribution in the different parts of the explant was uneven throughout the culture period. Callus tissue was the main site for accumulation of all these mineral elements.