Arbuscular mycorrhizal fungi influence water relations, gas exchange, abscisic acid and growth of micropropagated chile ancho pepper (Capsicum annuum) plantlets during acclimatization and post-acclimatization

Little is known about the role of arbuscular mycorrhiza fungi (AMF) on physiological changes of micropropagated plantlets during acclimatization and post-acclimatization. Using chile ancho pepper (Capsicum annuum L. cv. San Luis), measurements were made of water relations, gas exchange, abscisic acid (ABA), plantlet growth and AMF development. Plantlets had low photosynthetic rates (A) and poor initial growth during acclimatization. Relative water content (RWC) decreased during the first days after transfer from tissue culture containers to ex vitro conditions. Consequently, transpiration rates (E) and stomatal conductance (gs) declined, confirming that in vitro formed stomata were functional and able to respond ex vitro to partial desiccation--thus avoiding excessive leaf dehydration and plant death. Colonization by AMF occurred within 3 days after inoculation. Colonized plantlets had lower leaf ABA and higher RWC than noncolonized (NonAMF) plantlets during peak plant dehydration (6 days after plant transfer)--and a higher A and gs as early as days 5 and 7. During post-acclimatization [after day 8, when RWC increased and stabilized], A increased in all plantlets; however, more dramatic changes occurred with AMF plantlets. Within 48 days, 45% of the roots sampled of inoculated plantlets were colonized and had extensive arbuscule development. At this time, AMF plantlets also had greater E, A, leaf chlorophyll, leaf elemental N, P and K, leaf dry biomass and leaf area, fruit production and differences in carbon partitioning [lower root/shoot ratio and higher leaf area ratio] compared with NonAMF plantlets. Rapid AMF colonization enhanced physiological adjustments, which helped plantlets recover rapidly during acclimatization and obtain greater growth during post-acclimatization.     

影响喜树组织培养苗离体生根的因素

为了建立有效的喜树(Camptotheca acuminata)组培苗生根系统,提高其移栽成活率及适应性,用不同生长素种类及浓度、不同蔗糖浓度及不同培养基对喜树组培苗不定根形成影响以及移栽初期根系发育状况进行了研究。结果发现: 1)生长素种类和浓度明显影响喜树组培苗不定根形成,在含有IBA0.5 mg.L-1培养基中取得了最佳生根效果,生根率达到了98%,外植体平均生根数为5.9条/株; 2)不同浓度蔗糖对喜树组培苗生根也有一定影响,在10~30 g.L-1范围内,随着蔗糖浓度增加,生根百分率和生根数量都有增加,蔗糖浓度达到30 g.L-1时,生根百分率为95%,外植体平均生根数为5.4条/株; 蔗糖浓度在40 g.L-1时,表现出对生根抑制作用; 3)在基本培养基对喜树组培苗生根影响研究中发现,MS培养基对根形成表现出一定抑制作用;1/2MS和WPM培养基均适合喜树组培苗生根; 4)根系发育正常的喜树组培苗移栽后成活率可达96%,但组培苗根系根毛系统发育较差。组培苗单位叶面积根尖数量显著低于对照实生苗,而且此参数与叶片气孔导度呈显著正相关。这种较差根系发育导致叶片气孔导度过低可能是组培苗叶片光合能力较低的重要原因。     

影响喜树组织培养苗离体生根的因素

为了建立有效的喜树(Camptotheca acuminata)组培苗生根系统,提高其移栽成活率及适应性,用不同生长素种类及浓度、不同蔗糖浓度及不同培养基对喜树组培苗不定根形成影响以及移栽初期根系发育状况进行了研究.结果发现:1)生长素种类和浓度明显影响喜树组培苗不定根形成,在含有IBA0.5 mg·L-1培养基中取得了最佳生根效果,生根率达到了98%,外植体平均生根数为5.9条/株;2)不同浓度蔗糖对喜树组培苗生根也有一定影响,在10～30 g·L-1范围内,随着蔗糖浓度增加,生根百分率和生根数量都有增加,蔗糖浓度达到30 g·L-1时,生根百分率为95%,外植体平均生根数为5.4条/株;蔗糖浓度在40 g·L-1时,表现出对生根抑制作用;3)在基本培养基对喜树组培苗生根影响研究中发现,MS培养基对根形成表现出一定抑制作用;1/2MS和WPM培养基均适合喜树组培苗生根;4)根系发育正常的喜树组培苗移栽后成活率可达96%,但组培苗根系根毛系统发育较差.组培苗单位叶面积根尖数量显著低于对照实生苗,而且此参数与叶片气孔导度呈显著正相关.这种较差根系发育导致叶片气孔导度过低可能是组培苗叶片光合能力较低的重要原因.     

Nutritional and root development factors affecting growth of tissue culture plantlets of loblolly pine

Tissue culture plantlets of loblolly pine ( Pinus taeda L.) were compared to seedlings to quantify growth and developmental differences. The two plant types were grown in containers in a greenhouse and sampled periodically for twenty weeks. Dry weights and nitrogen and phosphorus concentrations of the shoots and roots were determined every two weeks.
During the twenty weeks in the greenhouse, seedlings grew to a greater size than the plantlets, but the relative rates of growth were approximately equal. Plantlets had significantly lower concentrations of nitrogen and phosphorus per g of shoot dry weight. Seedlings were much more efficient at nutrient uptake per g of dry weight of root. Plantlets had thick, unbranched roots, which were inefficient at nitrogen and phosphorus uptake. Nutrient uptake based on an index of root surface area was equal in the plantlets and seedlings.
The main differences between plantlets and seedlings apparently were related to root system morphology rather than physiological processes. The uptake of nutrients showed the greatest difference between the plant types.     

不同滴灌方式和NaCl处理对苹果幼树生长和水分传导的影响

为了探讨不同滴灌方式和土壤盐分对苹果(Malus pumila)幼树生长和水分传导(简称水分传导K)的影响。采用3种滴灌方式(交替滴灌(ADI, 根区两侧交替灌水)、固定滴灌(FDI, 根区固定一侧灌水)和常规滴灌(CDI, 根区两侧均灌水))和4个NaCl浓度梯度(0 (CK)、0.2% (S₁)、0.3% (S₂)、0.4% (S₃))。结果表明: 滴灌方式和NaCl浓度对苹果幼树生长和水分传导有显著影响。在相同的滴灌处理下, 随着NaCl浓度的增大, 苹果幼树的干物质、叶面积和净生长量及水分传导均显著地下降。根系水分传导(K_r)与总根干重间, 冠层水分传导(K_sh)与冠层干重间均呈显著的线性相关关系。在相同的NaCl处理下, 与CDI处理相比, ADI处理节水达50%, 平均根系干重、冠层干重、总干重、叶面积、净生长量和K_r仅分别下降了8.7%、19.24%、13.47%、11.87%、32.96%和10.72%; 这说明ADI处理对果树的生长和K_r具有明显的促进作用。在高盐分S₂和S₃处理下, ADI处理的叶水分传导(K_l+p)分别降低了33.56%和44.26%, 但ADI处理的K_r反而高出了CDI达1.13%和10.91%, 说明ADI处理增强了苹果幼树根源水力信号的传输效率和调控苹果幼树体内水分平衡的能力及抗盐分胁迫能力。ADI处理的生长状况和K_r均高于FDI。采用ADI处理进行灌溉不仅提高了节水调控能力, 而且也增强了抗盐分胁迫能力。     

Hormonal changes induced by partial rootzone drying of irrigated grapevine

Partial rootzone drying (PRD) is a new irrigation technique which improves the water use efficiency (by up to 50%) of wine grape production without significant crop reduction. The technique was developed on the basis of knowledge of the mechanisms controlling transpiration and requires that approximately half of the root system is always maintained in a dry or drying state while the remainder of the root system is irrigated. The wetted and dried sides of the root system are alternated on a 10-14 d cycle. Abscisic acid (ABA) concentration in the drying roots increases 10-fold, but ABA concentration in leaves of grapevines under PRD only increased by 60% compared with a fully irrigated control. Stomatal conductance of vines under PRD irrigation was significantly reduced when compared with vines receiving water to the entire root system. Grapevines from which water was withheld from the entire root system, on the other hand, show a similar reduction in stomatal conductance, but leaf ABA increased 5-fold compared with the fully irrigated control. PRD results in increased xylem sap ABA concentration and increased xylem sap pH, both of which are likely to result in a reduction in stomatal conductance. In addition, there was a reduction in zeatin and zeatin-riboside concentrations in roots, shoot tips and buds of 60, 50 and 70%, respectively, and this may contribute to the reduction in shoot growth and intensified apical dominance of vines under PRD irrigation. There is a nocturnal net flux of water from wetter roots to the roots in dry soil and this may assist in the distribution of chemical signals necessary to sustain the PRD effect. It was concluded that a major effect of PRD is the production of chemical signals in drying roots that are transported to the leaves where they bring about a reduction in stomatal conductance.     

Mycorrhizal fungi enhancement of growth and gas exchange of micropropagated guava plantlets (Psidium guajava L.) during ex vitro acclimatization and plant establishment

Psidium guajava L.) plantlets was determined during acclimatization and plant establishment. Guava plantlets were asexually propagated through tissue culture and grown in a glasshouse for 18 weeks. Half of the plantlets were inoculated with a mixed endomycorrhiza isolate from Mexico, ZAC-19, containing Glomus diaphanum, G. albidum and G. claroides. Plantlets were fertilized with modified Long Ashton nutrient solution that supplied 11 μg P ml⁻¹. Gas exchange measurements were taken at 2, 4, 8, and 18 weeks after inoculation using a portable photosynthesis system. All micropropagated guava plantlets survived transplant shock. After 6 weeks, mycorrhizal plantlets had greater shoot growth rates and leaf production than non-mycorrhizal plantlets. This also corresponded with increased photosynthetic rates and stomatal conductance of mycorrhizal plants. By 18 weeks, mycorrhizal plantlets had greater shoot length, leaf area, leaf, stem, and root dry mass. However, gas exchange was comparable among treatments, in part because the container size was restricting growth of the larger mycorrhizal plantlets. Non-mycorrhizal plantlets had greater leaf area ratios and specific leaf areas than mycorrhizal plantlets. Increased leaf tissue mineral levels of P, Mg, Cu, and Mo also occurred with mycorrhizal plantlets. Roots of inoculated guava plantlets were heavily colonized with arbuscules, vesicles and endospores. Guava plantlets were highly mycotrophic with a mycorrhizal dependency index of 103%. Accepted: 27 December 1999     

Comparative greenhouse study of Eucalyptus grandis in vitro plantlets and half-sib seedlings,II. Dry matter accumulation and relative distribution

In vitro directly micropropagated plantlets from three selected five-year-old Eucalyptus grandis Hill ex. Maiden hybrids were compared to their related half-sib seedlings for growth and growth pattern parameters under greenhouse conditions used for operational seedling production. The oven dry weights were determined from stem, leaf, and root samples collected every 40 days for four times. Relative growth rate, net assimilation rates and shoot:root ratio were calculated. Survival was 98% and 95% for plantlets and seedlings, respectively. Significant differences were observed between parents in terms of shoot and root dry weights and their ratios with similar ranking among plantlets and seedlings, suggesting genetic control over these traits. Plantlets started with significantly higher root: shoot ratios and stem, leaf, root, and total dry weight. Although seedlings had higher relative growth and net assimilation rates, all the initial differences decreased sharply over time.     

The effect of carbohydrate on the development of a Cattleya hybrid in association with its mycorrhizal fungus

To investigate beneficial effects of mycorrhizal fungi to advanced leafy orchids, growth studies on the development of symbiotic seedlings of the orchid Cattleya (aclandiae x schoeffeldiana) x aclandiae were conducted in vitro over a period of 18 months using split plates with minerals and carbohydrates on one side and water agar on the other. Mycorrhizal infection and shoot and root growth of seedlings on the nutrient side were compared to growth on the water agar side with nutrient uptake by the orchid only possible via external mycorrhizal hyphae. Seed germination was followed by mycorrhizal infection and rapid development of protocorms on both nutrient and non-nutrient sides of the plates. With 0.5% starch, development of protocorms was sustained for a least 12 weeks, compared to only 6 weeks with 0.1% starch. Advanced protocorms with two small leaves and a smoll root were transferred at week 22 to new fungal plates. When harvested at week 43, plantlets on 0.5% starch (both nutrient and water agar sides) had 2.7 times the dry weight of plantlets on 0.1% starch. Shoot-root ratios were higher on the lower level of carbon. In all plantlets, mycorrhizal infection involved less than 5% of the root length. With zero, 0.1% or 0.5% starch, the roots were re-infected on transfer to fresh fungal plates but young roots that developed following the transfer stayed free of infection, Plantlets on 0.5% starch (nutrient and water agar side) after 18 months had longer roots than plantlets grown in the absence of starch or on 0.1% starch. Shoots were small but significantly larger on the nutrient side than on the water agar side, independent of the carbohydrate level. The shoot-root ratio was highest on the nutrient side with no starch present. In this latter case, plantlet development was steady but plantlets on the non-nutrient side developed slowly; thus there was little evidence of nutrient translocation by the mycorrhizal fungus from the nutrient to the non-nutrient side in the absence of carbohydrates. Mycorrhizal infection is discussed as a mechanism for heterotrophic carbon assimilation. In advanced leafy orchids of Cattleya, external carbon resulted in increased root growth, decreased shoot/root ratio and sometimes yellowish-green plantlets.     

Leaf and root control of stomatal closure during drying in soybean

The stomatal conductance of an illuminated 2.5 cm² area of an intact soybean leaflet was the same whether the rest of the shoot was in light or darkness. This was true throughout soil drying cycles. Water potential of tissue immediately outside the illuminated area consistently decreased about 0.3 MPa upon illumination of the shoot. This erroneously suggested that stomatal conductance during soil drying did not respond to diurnal reductions in leaf water potential, but was controlled by root or soil water status. Tests showed that the water potential of tissue in the illuminated area did not change in the steady-state upon illumination of the rest of the shoot. Water potentials of shaded sections of leaves were not different from predawn water potentials, and were higher than leaf xylem pressure potentials as determined with a pressure chamber. These steep local gradients of leaf water potential suggest that there is minimal interchange of water among xylem elements leading from roots to different sections of leaves. The relationship between stomatal conductance and leaf water potential was the same whether leaf water potential was reduced by soil drying, application of polyethylene glycol (PEG) to the root system, lowering root temperature, or leaf excision. In the root cooling experiment, there was no soil drying, and with leaf excision, there was no root drying. The similarity of stomatal responses to leaf water potential in all cases strongly suggests control of conductance by a signal produced by local leaf water potential rather than root or soil water status in these experiments.     

In vitro sucrose concentration affects growth and acclimatization of <Emphasis Type="Italic">Alocasia amazonica</Emphasis> plantlets

Plantlets of Alocasia amazonica were regenerated on the MS medium supplemented with different concentrations (0–9%) of sucrose. An absence of sucrose in the growth medium induced generation of leaves, however, it decreased multiplication. On contrary, sucrose supply of 6% or 9% enhanced multiplication but hampered photoautotrophic growth (generation of leaves). Increasing sucrose supply also increased sugars and starch content and number of stomata and decreased water potential and size of stomata during in vitro growth period. During ex vitro acclimatization, shoot length, root length, leaf number and root number of Alocasia plantlets grown with 3% sucrose, were found to be better among the other studied sucrose concentrations. Under ex vitro acclimatization, number of stomata, contents of various carbohydrates in the leaves were increased but size of stomata decreased with increasing sucrose supply during in vitro growth period. Moreover, water potential of leaves of plantlets, which have been grown with a sucrose concentration other than 3%, was decreased. During in vitro growth, net CO₂ assimilation rate (P_N), transpiration (E), stomatal conductance (g_s) and variable fluorescence to maximum fluorescence ratio (Fv/Fm) were unaffected, however, during acclimatization these were changed and maximum P_N, E, and g_s were observed in the plantlets micropropagated with 3% sucrose. Fv/Fm was decreased severely in the plantlets micropropagated with 6% sucrose during acclimatization. Thus a sucrose concentration of 3% in the medium is appeared to be better among studied concentrations for both in vitro growth and ex vitro acclimatization of A. amazonica plantlets.     

Growth of Zea mays L. plants with their seminal roots only. Effects on plant development, xylem transport, mineral nutrition and the flow and distribution of abscisic acid (ABA) as a possible shoot to root signal

Maize (Zea mays L.) was grown in quartz sand culture eitherwith a normal root system (controls) or with seminal roots only(‘single-rooted’). Development of adventitious rootswas prevented by using plants with an etiolated mesocotyl andthe stem base was positioned 5–8 cm above the sand. Eventhough the roots of the single-rooted plants were sufficientlysupplied with water and nutrients, the leaves experienced waterdeficits and showed decreased transpiration as trans plrationalwater flow was restricted by the constant number of xylem vesselspresent in the mesocotyl. As a consequence of this restriction,transpirational water flow velocities in the metaxylem vesselsreached mean values of 270 m h^–1 and phloem transportvelocities of 5.2 m h^–1. Despite limited xylem transportmineral nutrient concentrations in leaf tissues were not decreasedin single-rooted plants, but shoot and particularly stem developmentwas somewhat inhibited. Due to the lack of adventitious rootsthe shoot:root ratio was strongly increased in the single-rootedplants, but the seminal roots showed compensatory growth comparedto those in control plants. Consistent with decreased leaf conductance,ABA concentrations in leaves of single-rooted plants were elevatedup to 10-fold, but xylem sap ABA concentrations in these plantswere lower than in controls, in good agreement with the well-wateredconditions experienced by the seminal roots. Surprisingly, however,ABA concentrations in tissues of the seminal roots of the single-rooted plants were clearly increased compared to the controls,presumably due to increased ABA import via phloem from the water-stressedleaves. The results are discussed in relation to the role ofABA as a shoot to root signal. Key words: Zea mays, seminal roots, plant development, xylem transport, mineral nutrition, ABA, shoot-to-root signal     

The influence of soil drought and partial waterlogging on water relations of Gmelina arborea seedlings

Summary Stomatal conductance of unstrossed, soil drought, and previously drought (predrought) Gmelina arborea seedlings increased in the morning and decreased before or immediately after midday. In the unstressed and predrought seedlings, leaf water potential decreased with increases in transpiration. In soil drought seedlings, there was some evidence of decreased hydraulic conductivity from soil to the plant, as indicated by the shape in the slope of the water potential/transpiration relationship. Root growth of drought plants was greater than in their unstressed counterparts at the lowest soil segment of a pot. The partial recovery of predrought seedlings was attributed to this subtantial root growth in the lowest soil segment.In the second experiment, Gmelina arborea seedlings were partially waterlogged, by flooding the polyethylene bag to half its length, for a period of 23 days. Waterlogging induced stomatal closure and reduction in leaf water potential but there was some evidence of tolerance to waterlogging towards the end of treatment. Root growth, shoot and root dry weights were slightly reduced below those of controls. After 9 days of waterlogging, adventitious roots began to form which correlated with depletion of soluble sugars in the shoot but with an increase in the roots.It is suggested that the tolerance of Gmelina plants to either soil drought or waterlogging may partly be due to partitioning of the soluble sugars from shoot to roots for production of roots and formation of adventitious roots respectively which are likely to enhance the flow of water from the soils to the plant. Therefore the plant response is very similar under conditions of increased deficits and surplus of soil water.     

Seedling vigour and the early growth of transplanted rice (Oryza sativa)

Previous studies suggest that the positive response of transplanted rice (Oryza sativa L.) to nursery fertiliser application was due to increased seedling vigour or possibly to increased nutrient content. This paper presents results of two glasshouse experiments designed to test the hypothesis that seedling vigour was responsible for the response of transplanted seedlings to nursery treatments. The aim of the present study was to explore the concept of seedling vigour of transplanted rice and to determine what plant attributes conferred vigour on the seedlings. Seedling vigour treatments were established by subjecting seedlings to short-term submergence (0, 1 and 2 days/week) in one experiment and to leaf clipping or root pruning and water stress in another to determine their effect on plant growth after transplanting. Submerging seedlings increased plant height but depressed shoot and root dry matter and root:shoot ratio of the seedling at 28 days after sowing. After transplanting these seedlings, prior submergence depressed shoot dry matter at 40 days. Nursery nutrient application increased plant height, increased root and shoot dry matter, but generally decreased root:shoot ratio. Pruning up to 60% of the roots at transplanting decreased shoot and root dry matter, P concentration in leaves at panicle initiation (PI) and straw dry matter and grain yield at maturity. By contrast, pruning 30% of leaves depressed shoot and root dry matter by 30% at PI, and root dry matter and straw and grain yield by 20% at maturity. The combined effects of leaf clipping and root pruning on shoot, root and straw dry matter were largely additive. It is concluded that the response of rice yield to nursery treatments is largely due to increased seedling vigour and can be effected by a range of nutritional as well as non-nutritional treatments of seedlings that increase seedling dry matter, nutrient content, and nutrient concentration. Impairment of leaf growth and to a lesser extent root growth in the nursery depressed seedling vigour after transplanting. However, rather than increasing stress tolerance, seedling vigour was more beneficial when post transplant growth was not limited by nutrient or water stresses.     

Acclimation to Drought in Acer pseudoplatanus L. (Sycamore) Seedlings

A glasshouse experiment was conducted with well-watered andwater-stressed seedlings of sycamore (Acer pseudoplatanus L.)grown in soil columns. Water was withheld when the seedlingswere 82-d-old. Effects of soil drying on stomatal behaviour,water relations, xylem cavitation, and growth of leaves androots were evaluated. Stomatal conductance declined well before any observable changein bulk leaf water potentials, and was correlated with soilwater status. At seven weeks, osmotic potential had declinedby 0·51 MPa and 0·44 MPa at full and zero turgor,respectively. Drought significantly increased both bulk elasticmodulus and leaf dry weight to turgid weight ratio of water-stressedplants. Drought had no effect on relative water content at zeroturgor. Water cavitation in the xylem was detected as ultrasonic acousticemissions (AE). Water-stressed plants displayed significantlyhigher rates of AE than well-watered plants. Maximum rate ofAE coincided with the minimum level of stomatal conductanceand apparent rehydration of the leaves. Drought caused changes in the root distribution profile andit increased the root weight. The increase in root weight wasmainly due to a substantial shift in assimilates allocated infavour of roots with total biomass being unaffected. Leaf growthwas maintained for six weeks without any significant declinein expansion rate. However, the development of severe waterstress reduced both leaf production and expansion.     

A comparative study on growth and morphology of wasabi plantlets under the influence of the micro-environment in shoot and root zones during photoautotrophic and photomixotrophic micropropagation

The growth of wasabi (Wasabia japonica Matsumura) plantlets under different micro-environments inside culture vessels in photoautotrophic micropropagation (PA) and photomixotrophic micropropagation (PM) conditions were compared. After 28 days of culture, dry weight, relative growth rate, leaf area, and leaf chlorophyll contents of plantlets in PA were greater than those in PM. The number of leaves did not differ significantly between PA and PM conditions. PA promoted root growth and development with a greater number of roots, root length, root diameter, root fresh weight, root dry weight, and root xylem vessel system. Dissolved oxygen concentration in PA culture medium sharply decreased after 7 days of culture and then recovered. In PM culture medium, no significant fluctuation of dissolved oxygen concentration was apparent. The net photosynthetic rates of plantlets in PA were much higher than those in PM and increased with culture time. In contrast, the net photosynthetic rates of wasabi plantlets in PM kept a low and constant value during the culture period. With the presence of gas exchange membranes attached to the vessel lids, the detected vapor pressure deficit was higher in PA than in PM conditions. Higher stomatal density and larger stomatal aperture on the abaxial and adaxial surfaces of the leaves in PM medium promoted leaf water loss following ex vitro conditions. Thus, PA is applicable for producing healthy wasabi transplants.     

Does Xylem Sap ABA Control the Stomatal Behaviour of Water-Stressed Sycamore (Acer pseudoplatanus L.) Seedlings?

Sycamore seedlings were grown with their root systems dividedequally between two containers. Water was withheld from onecontainer while the other container was kept well-watered. Effectsof soil drying on stomatal behaviour, shoot water status, andabscisic acid (ABA) concentration in roots, xylem sap and leaveswere evaluated. At 3 d, root ABA in the drying container increased significantly,while the root ABA in the unstressed container of the same plantsdid not differ from that of the control. The increase in rootABA was associated with the increase in xylem sap ABA and withthe decrease in stomatal conductance without any significantperturbation in shoot water status. At 7 d, despite the continuous increase in root ABA concentration,xylem sap ABA showed a marked decline when soil water contentwas depleted below 013 g g^–1. This reduction in xylemsap ABA coincided with a partial recovery of stomatal conductance.The results indicate that xylem sap ABA is a function of rootABA as well as the flow rate of water from roots to shoots,and that this ABA can be a sensitive indicator to the shootof the effect of soil drying. Key words: Acer pseudoplatanus L., soil drying, stomatal behaviour, xylem sap ABA     

土壤干旱条件下氮素营养对玉米内源激素含量影响

在田间持水量分别保持于35％、55％和75％±5％的土壤水分条件下,利用盆栽实验研究了土壤干旱和氮素营养对玉米内源激素和气孔导度的影响．结果表明,土壤干旱下氮素营养明显降低了玉米根系木质部汁液ABA浓度,而正常供水下施氮处理间则无显著差异(施氮处理仍较低),同时测定的叶片ABA浓度则呈相反的变化趋势,表现为干旱下施氮处理要高于不施氮处理;施氮处理木质部汁液中ZRs浓度应低于相应的不施氮处理,在调控气孔行为方面并未表现拮抗ABA作用;3种土壤水分条件下,施氮玉米叶片的气孔导度均高于不施氮处理,与木质部汁液ABA浓度呈负相关,说明施氮处理较低的根源ABA浓度是导致其气孔导度较大的主要原因．     

Use of gentian violet to differentiate in vitro and ex vitro-formed roots during acclimatization of grapevine

The dye gentian violet was added to culture medium in order to distinguish in vitro and ex vitro-formed roots during acclimatization of micropropagated plantlets. Shoots of the grapevine rootstock Kober 5BB were rooted on media containing the dye (0.3 and 0.15 mg·l^–1) for 3 weeks. The dye coloured the roots. Root length was reduced by the presence of the dye, but root number and shoot growth were not affected. Most in vitro-formed roots continued to grow during acclimatization, and 3 weeks after the transfer to soil the root system was 60% composed of in vitro-formed roots. Our results suggest that in grapevine Kober 5BB, the in vitro-formed roots contribute to plantlet growth at least during acclimatization.     

Root cooling strongly affects diel leaf growth dynamics,water and carbohydrate relations in Ricinus communis

In laboratory and greenhouse experiments with potted plants, shoots and roots are exposed to temperature regimes throughout a 24 h (diel) cycle that can differ strongly from the regime under which these plants have evolved. In the field, roots are often exposed to lower temperatures than shoots. When the root‐zone temperature in Ricinus communis was decreased below a threshold value, leaf growth occurred preferentially at night and was strongly inhibited during the day. Overall, leaf expansion, shoot biomass growth, root elongation and ramification decreased rapidly, carbon fluxes from shoot to root were diminished and carbohydrate contents of both root and shoot increased. Further, transpiration rate was not affected, yet hydrostatic tensions in shoot xylem increased. When root temperature was increased again, xylem tension reduced, leaf growth recovered rapidly, carbon fluxes from shoot to root increased, and carbohydrate pools were depleted. We hypothesize that the decreased uptake of water in cool roots diminishes the growth potential of the entire plant – especially diurnally, when the growing leaf loses water via transpiration. As a consequence, leaf growth and metabolite concentrations can vary enormously, depending on root‐zone temperature and its heterogeneity inside pots.