Roles of leaf in regulation of root and shoot growth from single node softwood cuttings of grape (Vitis vinifera)

The role of leaf in regulation of root and shoot growths in single node softwood cuttings of grape (Vitis vinifera) was characterised. Leafy cuttings showed early rooting, vigorous root growth and subsequent shoot development. Defoliation at planting induced early sprouting, but adversely affected rooting and decreased the survival of cuttings irrespective of pre‐planting treatment with 100 μM indole 3‐acetic acid (IAA). Treatment with IAA did not affect the percent rooting of leafy cuttings but increased root and shoot growth. Leaf weight (wt) and leaf area of the cuttings showed a highly significant correlation to root wt of the new plant at 4 wk after planting, while cutting stem + petiole wt was either not or less significantly correlated to root and shoot weights of the subsequent plant. The greater the area or wt of leaf, the better the root and shoot growths, implying that leaf contributed to adventitious root growth. However, retaining the leaf for just 2 days was enough to stimulate rooting in more than 80% of the cuttings, suggesting that leaf tissue could also induce root formation. Root growth increased with the period of leaf retention but leaf removal before 3 wk triggered sprouting leading to high mortality in rooted cuttings. Bringing the leaf closer to the rooting zone by preparing leaf at base (LAB) cuttings delayed rooting and sprouting compared with the standard leaf at top (LAT) cuttings. An inhibitory effect on rooting and sprouting by the exposed upper internode region in LAB cuttings is suggested.     

Leaf number and position effects on the survival and performance of grape microcuttings in vitro,and the sensitivity of the cut nodal region to the medium

The presence of leaf in microcuttings of grape cvs. Arka Neelamani and Thompson Seedless promoted rooting in vitro (MS, 1 μM IAA, 0.1 μM GA₃, 3% sucrose) but the effect varied depending on the number of leaves and position of the leaf on the cutting. Single node cuttings with a full-length lower internode and a lamina at top (LAT) showed earlier rooting and more root and shoot growth than cuttings with lamina positioned at the middle (LAM), while cuttings with a leaf at the base (LAB) of the cutting and full-length upper internode exhibited a lower percent rooting and sprouting, poor root and shoot growth, and low survival. Partial or complete removal of the upper internodal segment in LAB cuttings improved rooting and sprouting suggesting the possible operation of an inhibitory effect by the upper internode. Retaining an upper leaf in LAB cuttings (LAB+UL) resulted in necrosis of the upper leaf often followed by the lower one. The extent of necrotic damage was influenced by the leaf area and position or age of the cutting on the stock shoot. Retaining the lower internode in LAB and LAB+UL cuttings which held the node–leaf junction away from the medium, or reducing the concentration of MS medium helped significantly in improving the survival and performance of these cuttings. The difference in reaction between LAB and LAT cuttings was attributable mainly to the difference in the sensitivity of the stem part that came in contact with the medium. Removal of the leaf in LAB cuttings reduced this sensitivity. The majority of the LAB and LAB+UL cuttings, as well as non-rooting or delayed rooting LAT and LAM cuttings, exhibited high purple pigmentation of leaf, petiole and stem. Two-leafed cuttings in vitro showed poor survival, less rooting and low plantlet output compared to single-leafed cuttings. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of water stress mediated through agar on <Emphasis Type="Italic">in vitro</Emphasis> growth of potato

With the objective to develop a practical method of screening potato for drought tolerance, shoot and root growth in plantlets raised in vitro (from nodal cuttings drawn from in vivo as well as in vitro grown plantlets) were studied in three genotypes with known root mass production under field conditions. Different levels of water stress were induced using five concentrations of agar in MS (Murashige and Skoog in Physiol Plant 15:473–497, 1962) medium. Water potential of various media ranged from −0.70 MPa to −0.98 MPa. Water stress in culture adversely affected plantlet growth, and the responses varied with genotype and explant source. Genotype IWA-1 was less affected than Konafubuki and Norin-1. In the experiment with explants from in vivo grown plants, the time to rooting was considerably delayed in Konafubuki and Norin-1 by an increase in agar concentration, but no such effect was observed in IWA-1. In all media, the mean number of roots and root length was greater in IWA-1 than Konafubuki and Norin-1, and the latter two genotypes were at par. At 10 gl⁻¹ agar, IWA-1 had taller plantlets, heavier foliage dry weight, root volume, as well as root dry weight than Konafubuki and Norin-1, whereas the latter two genotypes were at par for all these characteristics. This pattern was similar to the reported pattern of these genotypes for root dry weight under field conditions. However, such similarity in the in vitro and field behavior of the tested genotypes was not observed when nodal cuttings drawn from in vitro plantlets were used as explants. It is concluded that in vitro screening of potato under specific and limited water stress conditions by raising plantlets from nodal cuttings drawn from in vivo grown plants may provide a system for effectively differentiating the genotypes for their expected root mass production under field conditions.     

Effects of sucrose concentration,supporting material and number of air exchanges of the vessel on the growth of in vitro coffee plantlets

Growth of coffee (Coffea arabusta) plantlets cultured in vitroas affected by sugar, types of supporting material and number of air exchanges of the vessel was investigated. Single node cuttings of in vitro coffee plantlets were cultured on half strength MS medium with or without 20 g l⁻¹ sucrose. Two types of supporting material, agar and Florialite, and two levels of air exchange expressed by number of air exchanges per vessel, 0.2 and 2.3 h⁻¹, were studied. At the end of a 40-day culture period, fresh weight, shoot length, root length and leaf area of plantlets when cultured on Florialite soaked in sugar-free medium and under the higher number of air exchanges were greater than those in sugar containing medium. Callus was observed at the shoot base of plantlets grown on agar medium containing sucrose. Photosynthetic ability of coffee plantlets in vitro was also significantly increased when grown on sugar-free medium with the high number of air exchanges and Florialite as a supporting material. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of vitamins on sprouting of purple nutsedge tubers

Vitamins of the B group and vitamin C were applied to purple nutsedge (Cyperus rotundus L.) tubers to study their effect on the sprouting rate, initiation and establishment of sprouts, growth of plantlets and development of orthotropic rhizomes in comparison with the corresponding effects of kinetin. Ascorbic acid up to 100 mg I^?1 hastened sprouting, whereas vitamins of the B group and kinetin retarded sprouting; 100% tubers sprouted in all treatments within 10 days. Unlike kinetin, none of the vitamins resulted in the establishment of more than one sprout per tuber. Riboflavin and pyridoxine promoted root and shoot growth of the plantlets, whereas kinetin produced short, thick shoots and inhibited root growth, with increasing concentration. Ascorbic acid was only second to kinetin in the induction of orthotropic rhizomes, but the former resulted in an increase in rhizome length.     

Direct shoot regeneration from node,internode, hypocotyl and embryo explants of Withania somnifera

In vitro studies were initiated with Withania somnifera (L.) Dun. for rapid micropropagation of selected chemotypes using nodes, internodes, hypocotyls and embryo explants. Direct regeneration of shoot buds was observed in MS basal medium supplemented with various concentrations of either benzyladenine (BA) or thidiazouron (TDZ) depending on the explant. Nodal explants formed multiple shoots both from pre-existing and de novo buds on Murashige and Skoog's medium (MS) containing 0.1–5.0 mg l⁻¹ BA and a ring of de novo shoot buds on MS medium containing 0.2 and 0.3 mg l⁻¹ TDZ. Internodal explants formed shoot buds on MS with 1.0 and 5.0 mg l⁻¹ BA while the hypocotyl explants gave rise to multiple shoots only on MS with 0.5 mg l⁻¹ BA. Isolated embryos gave rise to many shoot buds on MS with 0.2 and 0.3 mg l⁻¹ TDZ. The shoot buds elongated and rooted either on MS medium with 0.01 mg l⁻¹ BA or on half strength MS medium lacking growth regulators, which depended upon the growth regulator used in the shoot bud induction medium. Except for the embryo-derived plantlets, all other plantlets could be acclimatized with 100% success. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of sucrose application,minerals, and irradiance on the <Emphasis Type="Italic">in vitro</Emphasis> growth of <Emphasis Type="Italic">Cistus incanus</Emphasis> seedlings and plantlets

To study the effect of sucrose on the sink-source relationship in in vitro-grown plants, Cistus incanus seedlings and plantlets were grown horizontally in a two-compartment Petri dish (split dish), with the root system in one compartment and the shoot in the other. Shoots and roots were exposed to different sucrose concentrations (0–30 g dm⁻³), two irradiance levels (25 and 160 μmol m⁻²s⁻¹) and the presence or absence of a minimum medium containing minerals and vitamins (M medium). Root and shoot biomass of the seedlings was enhanced by an increase in irradiance when the growth medium was not supplemented with sucrose indicating the role of photosynthesis in biomass production. When sucrose was added to either organ growth was enhanced as well. In the presence of sucrose in the root compartment, sucrose applied to the shoot compartment enhanced growth of both organs under low irradiance, while under high irradiance, sucrose had no further additive effect. In the absence of sucrose in the root compartment, the enhancement of root biomass by sucrose added to the shoot compartment was lower under high irradiance than under low irradiance. The response of Cistus plantlets to sucrose and irradiance differed from that of seedlings, probably reflecting a greater susceptibility of the plantlets to sucrose feedback inhibition on photosynthesis and biomass accumulation. The decrease in root and shoot growth when M medium was added to the shoot compartment and the relatively better growth of these organs when the roots were supplied with minerals and the shoot with sucrose, indicate that growth of the two organs in our experimental set-up was regulated by opposing fluxes of C and nutrients.     

Establishment of Camptotheca acuminata regeneration from leaf explants

Plantlet regeneration through shoot formation from young leaf explant-derived callus of Camptotheca acuminata is described. Calli were obtained by placing leaf explants on Woody plant medium (WPM) supplemented with various concentrations of 6-benzyladenine (BA) and naphthaleneacetic acid (NAA) or 2,4-dichlorophenoxyacetic acid (2,4-D). Callus induction was observed in all media evaluated. On the shoot induction medium, the callus induced on the WPM medium containing 19.8 μM BA and 5.8 μM NAA was the most effective, providing high shoot regeneration frequency (70.3 %) as well as the highest number of shoots (11.2 shoots explant⁻¹). The good rooting percentage and root quality (98 %, 5.9 roots shoot⁻¹) were achieved on WPM medium supplemented with 9.6 μM indole-3-butyric acid (IBA). 96 % of the in vitro rooted plantlets with well developed shoots and roots survived transfer to soil.     

Phloroglucinol enhances growth and rate of axillary shoot proliferation in potato shoot tip cultures in vitro

Efficacy of phloroglucinol in promoting growth and development of in vitro-derived shoot tips was studied in six potato (Solanum tuberosum L.) genotypes. Different concentrations of phloroglucinol (0, 0.08, 0.4, 0.8, 1.2 and 1.6 mM) were tested in combination with either 0.1 or 0.2 M sucrose in shoot tip proliferation medium based on MS (Murashige and Skoog, 1962) medium supplemented with 5.8 μM GA₃ (gibberellic acid), 1.1 μM BA (N⁶-benzyladenine) and 8.39 μM D-calcium pantothenate. Phloroglucinol fostered multiple shoot formation, promoted axillary shoot proliferation in terms of shoot tip fresh weight and shoot length, and stimulated root formation on the shoot tips. There was significant phloroglucinol × sucrose interaction for number of shoots developed per shoot tip, shoot tip fresh weight and number of roots induced per shoot tip. The beneficial effect of phloroglucinol on shoot tip survival was conspicuous only in genotypes that showed poor survival in the control proliferation medium. There were significant differences in response between the two sucrose levels with regard to shoot tip fresh weight and number of roots per shoot tip. Phloroglucinol in combination with 0.2 M sucrose induced maximum number of roots per shoot tip. Optimum shoot tip growth was fostered in medium containing 0.8 mM phloroglucinol and 0.2 M sucrose. High frequency multiple shoot formation in this medium ensures a faster rate of potato shoot tip multiplication within a limited time and space. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photoautotrophic growth response of in vitro cultured coffee plantlets to ventilation methods and photosynthetic photon fluxes under carbon dioxide enriched condition

Effects of two ventilation methods (forced and natural) and two photosynthetic photon fluxes (PPF, 150 and 250 μmol m⁻² s⁻¹) on the photoautotrophic growth of in vitro cultured coffee (Coffea arabusta) plantlets were investigated. Number of air exchanges was 2.7, 5.9 and 3.9 h⁻¹ for forced low rate, forced high rate and natural ventilation, respectively. Single node cuttings of in vitro cultured coffee plantlets were cultured on Florialite, a mixture of vermiculite and cellulose fibers with high air porosity, emerged in liquid half strength basal MS medium, without sucrose, vitamins and plant growth regulators. The study included 40 days in the in vitro stage and 10 days in the ex vitro stage. Mean fresh and dry weights, leaf area, shoot and root lengths and net photosynthetic rate per plantlet were significantly greater in forced high rate treatments compared with those in natural and forced low rate treatments. PPF had a distinct effect on shoot length suppression and root elongation of coffee plantlets in forced high rate treatments. The control of carbon dioxide concentration inside the culture box according to the plant demand when growing was easy with the forced ventilation method in photoautotrophic micropropagation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Promoting root induction and growth of in vitro macadamia (<Emphasis Type="Italic">Macadamia tetraphylla</Emphasis> L. ‘Keaau’) plantlets using CO<Subscript>2</Subscript>-enriched photoautotrophic conditions

In this study, a rooting protocol was developed for macadamia plantlets with healthy roots and enhanced growth performance, along with enhanced photosynthetic capability. In vitro-grown shoots rooted in vented vessels containing vermiculite as the supporting material exhibited 100% frequency of root induction, whereas when shoots were grown in non-vented vessels containing a solidified Murashige and Skoog (MS) medium, the frequency of root induction was less than 30%. The formation of root with callus, hyperhydricity, and leaf necrosis was observed in this photomixotrophic closed system. The modification of the vented photoautotrophic system with different concentrations of CO₂ and sucrose were investigated using vermiculite as the supporter. The number of roots, root length, root surface area, fresh weight, and dry weight were significantly higher in plantlets grown in CO₂-enriched (1,000 μmol CO₂ mol⁻¹) photoautotrophic conditions. The water content in both root and shoot tissues of plantlets cultured under photoautotrophic conditions was maximized. In addition, shoot and leaf performances were enhanced in plantlets cultured under CO₂-enriched photoautotrophic conditions. The supplementation of sucrose (29–88 mM) to culture media in both ambient and elevated CO₂ conditions affected a reduction in the shoot and root performance of in vitro plantlets. Chlorophyll a, chlorophyll b, and total carotenoids in the leaf tissues of plantlets acclimatized in CO₂-enriched photoautotrophic conditions were enriched, leading to increasing photosynthetic abilities, including chlorophyll fluorescence and net photosynthetic rate. From this investigation, a root induction protocol was established and the production of healthy macadamia plantlets was successfully implemented using CO₂-enriched photoautotrophic conditions.     

Periodicity in the development of the root system of young rubber trees (Hevea brasiliensis Müell. Arg.): relationship with shoot development

The growth pattern of the root system of young rubber trees (Hevea brasiliensis) was studied in relation to shoot development over a period of 3 months. Temporal and spatial variations in elongation and branching processes were examined for the different root types, by means of root observation boxes. Shoot growth was typically rhythmic. Root development was periodic and related to leaf expansion. Root elongation was depressed during leaf growth, whereas branching was enhanced. Consequently, highly branched areas with vigorous secondary roots alternated along the taproot with poorly branched areas with shorter roots. Root types were not affected to the same degree by shoot competition: during leaf expansion, taproot growth was just depressed but remained continuous, the emergence and elongation rates of secondary roots were significantly affected and the elongation rates of tertiary roots fell to zero. These results were consistent with the hypothesis that root growth is related to competition for assimilates and to the sink strength of the different root types, whereas root branching appeared to be promoted by leaf development.     

Aluminum inhibition of shoot lateral branches ofGlycine max and reversal by exogenous cytokinin

Aluminum effects on the morphological development of soybean (Glycine max (L.) Merr.) were characterized in greenhouse and growth chamber experiments. An Al-sensitive cultivar, ‘Ransom’, was grown in an acid soil (Aeric Paleudult) adjusted to 3 levels of exchangeable Al. Lateral shoot development at the nodes of the main stem was extensive in the limed soil containing 0.06 cmol(+) Alkg⁻¹. However, lateral shoot length and weight were severely inhibited in the unlimed soil containing 2.19 cmol(+) Alkg⁻¹, and in the unlimed soil amended to 2.63 cmol(+) Alkg⁻¹ with AlCl₃. This inhibition by the high Al/low pH condition was reversed by the exogenous application of a synthetic cytokinin 6-benzylaminopurine (BA). The daily application of 20 μg mL⁻¹ BA applied locally to the lateral meristems of plants grown in the unlimed soil stimulated lateral shoot growth substantially, such that it was either comparable to or greater than that observed in the limed treatment without BA. Accumulation of K, Ca, and Mg in lateral shoot branches was also stimulated by the local application of BA. The inhibitory effects of Al on lateral shoot development were confirmed in solution culture. In addition, differential sensitivity to Al was evident among the primary root, first order lateral roots, and second order lateral roots. The length of the primary root was only slightly decreased by increasing concentrations of Al up to 30 μM. In contrast, the length of basipetally located first order lateral roots was restricted to greater extent; up to 50% by 30 μM Al. Second order lateral lengths were inhibited even more severely; up to 86% by 30 μM Al. Substantial evidence in the literature indicates that the root apex is a major site for the biosynthesis of cytokinin that is supplied to shoots, and cellular function and development in this region of the root are impaired during Al toxic conditions. This suggests that one mode of action by which Al may affect shoot growth is by inhibiting the synthesis and subsequent translocation of cytokinin to the meristematic regions of the shoot. The present observation of a reversal of Al-inhibited lateral shoot development by exogenously applied cytokinin supports this hypothesis. However, the inability of applied cytokinin to counter the restriction imposed by Al on total shoot dry matter production implies the impairment by Al toxicity of other root functions, such as ion and water transport, also played an important role in altering shoot morphology.     

TDZ-induced high frequency plant regeneration through multiple shoot formation in witloof chicory (<Emphasis Type="Italic">Cichorium intybus</Emphasis> L.)

A very efficient and rapid regeneration system via multiple shoot formation was developed for Cichorium intybus L. when leaf explants excised from sterile seedlings were cultured on medium supplemented with different concentrations and combinations of various plant growth regulators. In a comparison of leaf lamina and petiole explants, lamina explants produced over three times more shoots than petiole explants, with a mean of 7.5 shoots compared to 2.4. Of the combinations of KIN/IAA, KIN/NAA, BAP/IAA, or BAP/NAA, 0.5 mg l⁻¹ KIN combined with 0.3 mg l⁻¹ IAA was the most effective, producing a mean of 19.7 shoots per lamina explant while the control treatment involving no plant growth regulators produced no shoots at all. When either cytokinin was used alone, BAP was found nearly twice more successful than KIN. However, the most effective treatment of all was the combination of 0.01 mg l⁻¹ TDZ and 1.0 mg l⁻¹ IAA, producing as many as 35.8 shoots per lamina explant. This rate of shoot regeneration is remarkably higher than those previously reported for C. intybus, most likely due to the highly inductive effect of TDZ, which was tested for the first time in this species. Rooting of the shoots was readily achieved on medium containing different concentrations of IAA or IBA. IAA was more effective than IBA and resulted in the highest frequency of shoots that rooted (100%) and mean number of roots per shoot (4.2) when used at 0.5 mg l⁻¹. Hardening off process resulted in a production of more than 80% healthy plantlets.     

In vitro culture of <Emphasis Type="Italic">Hibiscus rosa-sinensis</Emphasis> L.: Influence of iron,calcium and BAP on establishment and multiplication

Some factors influencing in vitro cultures of potted Hibiscus rosa-sinensis L. using nodal cuttings were investigated. A protocol using a modified MS medium helped to overcome chlorosis, shoot tip necrosis (STN) and leaf drop. These disorders have been caused by mineral imbalance associated with calcium and iron deficiency. STN and leaf drop were overcome by increasing calcium level from 3 mM (MS standard concentration) to 9 mM, and this increase, in addition, enhanced shoot dry weight and shoot extension. The chlorophyll content and leaf area increased by increasing the iron concentration 3-fold from 98 μM to 295 μM. Furthermore, substituting Fe-EDTA with Fe-EDDHA resulted in an increase in chlorophyll content, leaf area and shoot extension. The most suitable multiplication medium for H. rosa-sinensis L. was demonstrated to be a modified MS medium containing 2.2 μM BAP and increased concentrations of calcium at 9 mM and iron at 295 μM provided as Fe-EDDHA. The shoots were rooted in half-strength modified MS medium containing 2.7 μM NAA. Acclimatization was successful with all shoots with or without roots.     

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     

Effect of DTNB on glutamate dehydrogenase activity in root and shoot extracts of maize seedlings

NADH specific glutamate dehydrogenase (GDH) activity was examined in roots and shoots of maize seedlings grown in half-strength Hoagland’s solution containing NH₄NO₃ as sole nitrogen source under irradiance of 60 W m⁻² and temperature of 25±2°C. When 5,5′-dithio-bis (2-nitrobenzoic acid) (DTNB) was supplied to the assay mixture, it inhibited NADH-GDH activity in both roots and shoots, irrespective of whether the enzymes were extracted from light- or dark-treated roots and shoots. In each case the inhibition increased with the increase in DTNB concentration. At the maximum concentration of DTNB used (20 μM) the inhibition of shoot NADH-GDH was more pronounced than inhibition of root enzyme. This indicated differences in shoot and root NADH-GDH.     

Role of VA-mycorrhiza in growth and mineral nutrition of apple (Malus pumila var.domestica) rootstock cuttings

One-year-old apple cuttings (Malus pumila var.domestica cv. M26) were grown for 6 months in pot culture with and without inoculum of the VA-mycorrhizal fungus (VAMF)Glomus macrocarpum in soil from a long-term fertilizer field experiment with different P availability (20, 210, and 280 mg CAL-extractable P kg⁻¹). The indigenous VAMF propagule density was reduced by 0.5 Mrad X-irradiation. At harvest, non-inoculated and inoculated plants had similar proportions of root length bearing vesicles. Net dry weight of tree cuttings was significantly increased by inoculation only at 20 mg P kg⁻¹ (+62%). Increasing P availability from 210 to 280 mg P kg⁻¹ led to a 4-week depression of shoot elongation rate only in the inoculated plants. Uptake of P was significantly enhanced by inoculation at 20 and 210 mg P kg⁻¹ (+64 and +12%, respectively). On average, inoculated plants had significantly higher concentrations of Zn in leaves and in roots (+16 and +14%, respectively) and of copper in stems and in roots (+13 and +126%, respectively). Proportion of vesicle bearing root length was significantly correlated with root caloric content. A lipid content of 0.9–4.5% in the root dry matter was attributed to the presence of vesicles corresponding to 1.6–8.2% of total root caloric content. As the control plants were also infected, the beneficial effect of VA-mycorrhiza on nutrient uptake and growth of apple cuttings was underestimated at all P levels. Furthermore, VAM-potential at the lowest P level was not fully exploited as onset of infection was most certainly delayed because of a decreased photosynthetic rate due to P deficiency. Energy drain by VAMF-infection was most probably underestimated considerably, due to, among others, loss of infected root cortex during root growth, sampling and staining. It is concluded that apple cuttings rely on VA-mycorrhizal P-uptake at least in low P soils. In high P soils, apple cuttings may profit predominantly from the uptake of Zn and Cu by the fungal symbionts.     

Adverse Effect of Shoot Growth on Root Growth in Rooted Cuttings of Aspen

In experiments with rooted cuttings of aspen (Populus tremula L). with a small leaf area, it was found that the roots grew well as long as there was no shoot growth. The onset of shoot growth was followed by a period of decreased root growth. When the leaf area had increased sufficiently, root growth recovered. Decreasing the shoot growth by removal of growth points in the shoot or by short day treatment increased the fraction of photosynthesis products used for root growth, leading to increased root/shoot ratios. Competition between growing shoots and roots for carbohydrates formed in photosynthesis is considered to cause the effects noted and to be of importance for maintaining the balance between the root and shoot systems.     

Growth, morphogenesis, and essential oil production in Mentha spicata L. plantlets in vitro

To date, plantlet culture has not been explored as a means to obtain secondary metabolites in vitro. However, plantlets readily produce desirable secondary metabolites, which may not be produced in cell suspension or callus cultures. To optimize plantlet growth in vitro, the influences of various physical environments on the growth (fresh weight), morphogenesis (leaf, root, and shoot number), and volatile carbon metabolites (i.e. monoterpene, (−)-carvone) of Mentha spicata L. (spearmint) plants were studied. The carvone content in different portions of sterile plantlets was analyzed. Carvone was only produced from the foliar regions of cultured plantlets and was absent in the callus and roots. The influence of physical support (e.g., agar, glass gravel, liquid, platform or sponge), frequency of media replacement, and culture vessel capacity on spearmint plantlets growth and carvone production was tested. A comparative study was conducted testing the growth, morphogenesis, and secondary metabolism occurring with three different spearmint cultivars grown in either culture tubes containing 25 ml agar medium or in an automated plant culture system (APCS; a sterile hydroponics system) employing a 1-l medium reservoir. Increasing the number of media immersions (4, 8, 12 or 16 immersions d⁻¹) of plantlets growing in the APCS increased growth and morphogenesis responses. Generally, higher culture growth rates resulted in lower carvone treatment⁻¹ (mg carvone g-FW⁻¹); however, overall total carvone ((mg carvone g-FW⁻¹) × g culture FW) increased because of the production of greater biomass obtained per vessel.