Leaf Thickness and Water Deficit in Plants: A Tool for Field Studies

B?rquez, A. 1987. Leaf thickness and water deficit in plants:a tool for field studies.—J. exp. Bot. 38: 109–114. A technique for estimating plant water deficits using a relativelyinexpensive micrometer to measure leaf thickness was developed.A strong correlation was found between leaf thickness and relativewater content (RWC) in Brassica napus, Mirabilis jalapa, Phaseolusvulgaris and Impatiens parviflora. Although leaf thickness ata given RWC varied between plants, it increased linearly withleaf RWC, the rate of change being similar in leaves of plantsof the same age and species. Due to this relationship, the constructionof a pressure-volume curve makes possible the estimation ofleaf water potential. In this case a calibration curve is neededfor each population studied or, for the highest accuracy, foreach individual. The technique is particularly useful in fieldconditions where other techniques are not reliable because ofdifficulties in controlling temperature and where non-destructivemeasurements are required. Key words: Leaf thickness, relative water content, water potential     

The Influence of Resaturation Method and Tissue 3Quercus alba L. Seedlings

Parker, W. C. and Pallardy, S. G. 1987. The influence of resaturationmethod and tissue type on pressure-volume analysis of Quercusalba L. seedlings.—J. exp. Bot. 38: 535–549. The effect of resaturation method and amount of woody tissueon pressure-volume analysis was investigated using materialcollected from Quercus alba L. seedlings. Leaves excised fromwell-irrigated, intact plants had lower initial xylem pressurepotentials than did leaves resaturated by two artificial methods.Differential capacity for tissue rehydration among the threemethods was linked to shifts in the relative position of pressure-volumecurves, and differences in the osmotic potential and relativewater content at which turgor loss occurred were observed. Pressure-volumecurves from leaves resaturated by all three methods contained‘plateaus’ near full turgor, where xylem pressurepotential declined only slightly with relative water content.These plateaus were apparently associated with apoplastic waterthat accumulated in intercellular spaces of the leaf near fullturgidity, and acted to buffer changes in leaf xylem pressurepotential as tissues dehydrated. The presence of this waterhas implications for derived water relations parameter estimates.Pressure-volume curves for excised shoots also exhibited plateaus,but the relationship between xylem pressure potential and relativewater content over this region was steeper than was found forleaves. Shoot osmotic potentials were somewhat lower than thosefor leaves. The slope of the linear portion of shoot pressure-volumecurves was more shallow than for single leaves, a response associatedwith comparatively lower values of the symplastic water fractionin shoots. Key words: Pressure-volume curve, tissue-water relations, elasticity     

Changes in Chlorophyll Content and Organization During Senescence of the Primary Leaves of Phaseolus vulgaris L. in Relation to Photosynthetic Electron Transport

A large decrease was observed in the chlorophyll content ofthe primary leaves of Phaseolus vulgaris during senescence.Chloroplasts isolated from mature and senescent leaves gavevery similar light saturation curves for electron transportreactions involving either PS I or PS II, indicating that theaverage number of chlorophyll molecules associated with eachreaction centre did not change during senescence. It is concludedthat the reaction centres ceased to function at the same timeas, or perhaps before, their antenna chlorophylls were lostfrom the thylakoid membrane, and that the percentage decreasein the number of functional reaction centres per leaf was atleast as great as the percentage decrease in the leaf chlorophyllcontent. The chlorophyll-protein composition of thylakoid membrane preparationswas examined by electrophoresis of samples treated with sodiumdodecyl sulphate. In older leaves a smaller proportion of thechlorophyll applied to polyacrylamide gels was associated withthe P700- chlorophyll a-protein complex. There was also a declinein emission at 734 nm in the 77 °K fluorescence spectrumof intact leaf tissue during senescence. These results indicatethat older leaves contained a smaller proportion of chlorophyllsassociated with PS I, and this is consistent with the decreaseobserved in the leaf chlorophyll a/b ratio during senescence.The effect of these changes in chlorophyll content on the capacityof the chloroplast to carry out photosynthetic electron transportis discussed.     

Are Mistletoes Shade Plants? CO2Assimilation and Chlorophyll Fluorescence of Temperate Mistletoes and their Hosts

Mistletoes usually have slower rates of photosynthesis thantheir hosts. This study examines CO₂assimilation, chlorophyllfluorescence and the chlorophyll content of temperate host–parasitepairs (nine hosts parasitized by Ileostylus micranthus and Carpodetusserratus parasitized by Tupeia antarctica). The hosts of I.micranthus had higher mean annual CO₂assimilation (3.59 ±0.41 µmol m^-2 s^-1) than I. micranthus(2.42 ± 0.20µmol m^-2 s^-1), and C. serratus(2.41 ± 0.43 µmolm^-2 s^-1) showed higher CO₂assimilation than T. antarctica(0.67± 0.64 µmol m^-2 s^-1). Hosts saturated at significantlyhigher electron transport rates (ETR) and light levels thanmistletoes. The positive relationship between CO₂assimilationand electron transport suggests that the lower CO₂assimilationrates in mistletoes are a consequence of lower electron transportrates. When photosynthetic rates, ETR and chlorophyll a /b ratioswere adjusted for photosynthetically active radiation, hostsdid not have significantly higher CO₂assimilation (3.21 ±0.37 µmol m^-2 s^-1) than mistletoes (2.54 ± 0.41µmol m^-2 s^-1), but still had significantly higher ETRand chlorophyll a / b ratios. The electron transport rates,saturating light and chlorophyll a / b ratios of sun leavesfrom mistletoes were similar to host shade leaves. These responsesindicate that in comparison with their hosts, mistletoe leaveshave the photosynthetic characteristics of the leaves of shadeplants. Copyright 2000 Annals of Botany Company CO₂assimilation, photosynthetic active radiation (PAR), chlorophyll fluorescence, electron transport rate (ETR), photochemical quenching (q_p), non-photochemical quenching (q_n), sun and shade leaves, chlorophyll content, Ileostylus micranthus, Tupeia antarctica, New Zealand     

Patterns of Protein Synthesis in Lolium temulentum (L.): I. CHANGES OCCURRING DURING LEAF DEVELOPMENT

The course of amino-acid incorporation was followed during successivephases of leaf development in third and fifth leaves of Loliumtemulentum(L.) growing under 8- and 16-h photoperiods. Threepeak periods of protein synthesis were recognized during thelife span of the leaf. The first coincided with leaf expansionand reflected the formation of photosynthetic enzymes whilethe second occurred in the fully expanded leaf and was associatedwith increases in alanine aminotransferase, malate dehydrogenase,and peroxidase. A third incorporation maximum coincided withthe onset of senescence, possibly representing the elaborationor release of degradative enzymes. The positioning of the firstand third protein-synthesis peaks was sensitive to photoperiodbut the second maximum tended to occur at a fixed point afterleaf emergence. Changes during the ‘greening-up’of etiolated leaves are also described. An over-all correlation coefficient of +0.81 was obtained forthe relationship between chlorophyll content and alanine aminotransferaseactivity. The data are discussed in relation to the existenceof pre-programmed sequences in leaf development.     

SPAD chlorophyll meter reading can be pronouncedly affected by chloroplast movement

Non-destructive assessment of chlorophyll content has recently been widely done by chlorophyll meters based on measurement of leaf transmittance (e.g. the SPAD-502 chlorophyll meter measures the leaf transmittance at 650 and 940 nm). However, the leaf transmittance depends not only on the content of chlorophylls but also on their distribution in leaves. The chlorophyll distribution within leaves is co-determined by chloroplast arrangement in cells that depends on light conditions. When tobacco leaves were exposed to a strong blue light (about 340 μmol of photons m⁻² s⁻¹), a very pronounced increase in the leaf transmittance was observed as chloroplasts migrated from face position (along cell walls perpendicular to the incident light) to side position (along cell walls parallel to the incoming light) and the SPAD reading decreased markedly. This effect was more pronounced in the leaves of young tobacco plants compared with old ones; the difference between SPAD values in face and side position reached even about 35%. It is shown how the chloroplast movement changes a relationship between the SPAD readings and real chlorophyll content. For an elimination of the chloroplast movement effect, it can be recommended to measure the SPAD values in leaves with a defined chloroplasts arrangement.     

Identification of Hinesol as a Chlorophyll-Preserving Substance

A chlorophyll-preserving substance was isolated from rhizomesof Atractylodes lancea DC. and identified as (—)-hinesolon the basis of spectroscopic data. Hinesol at more than 0.22DIH was effective for preserving chlorophyll of oat (Avena sativaL. cv Victory) leaves in the dark with 40 to 50% of the initialchlorophyll content being retained at 2.2 mM. However, hinesolstimulated chlorophyll loss with light exposure and at 4.5 mMcaused complete bleaching when measured 4 days after treatment. ¹Dedicated to the memory of the late Professor Joji Ashida. (Received December 9, 1982; Accepted April 22, 1983)     

Leaf Characteristics and Net Gas Exchange of Diploid and Autotetraploid Citrus

The effect of tetraploidy on leaf characteristics and net gasexchange was studied in diploid (2x ) and autotetraploid (4x) ‘Valencia’ sweet orange (Citrus sinensis (L.)Osb.) and ‘Femminello’ lemon (Citrus limon (L.)Burm. f.) leaves. Comparisons between ploidy levels were madeunder high irradiance (I) in a growth chamber or low total Iin a glasshouse. Tetraploids of both species had thicker leaves,larger mesophyll cell volume and lower light transmittance thandiploids regardless of growth I. Mesophyll surface area perunit leaf area of 2x leaves was 5–15% greater than on4x leaves. Leaf thickness and mesophyll cell volume were greaterin high I leaves than low I leaves. In high I, average leafarea was similar for 2x and 4x leaves, whereas in low I it was30% greater in 4x than in 2x leaves. Nitrogen and chlorophyllconcentration per cell increased with ploidy level in both growthconditions. The ratio of chlorophyll a:b was 25% greater in2x than in 4x leaves. When net CO₂assimilation rate (A_CO2) wasbased on leaf area, 4x orange leaves had 24–35% lowerA_CO2than their diploids. There were no significant differencesin A_CO2between 2x and 4x orange or lemon leaves when expressedon a per cell basis. Overall, lower A_CO2per unit leaf area oftetraploids was related to increase in leaf thickness, largermesophyll cell volume, the decrease in mesophyll area exposedto internal air spaces, and the lower ratio between cell surfaceto cell volume. Such changes probably increased the resistanceto CO₂diffusion to the site of carboyxlation in the chloroplasts. Cell volume; chlorophyll; irradiance; leaf thickness; nitrogen; photosynthesis; ploidy; Citrus limon ; C. sinensis ; ‘Valencia’ sweet orange; ‘Femminello’ lemon     

Acclimation of Tomato Leaves to Changes in Light Intensity; Effects on the Function of the Thylakoid Membrane

When young tomato plants grown in high light (400 µmolquanta m^–2s^–1 PAR) were transferred to low light(100 µmol quanta m^–2s^–1 PAR), non-cyclic electrontransport capacity was decreased and the rate of dark re-oxidationof Q^–, the first quinone electron acceptor of photosystemII, was decreased within 1–2 d. In contrast, the amountof coupling factor CF₁, assayed by its ATPase activity, decreasedmore gradually over several days. The total chlorophyll contentper unit leaf area remained relatively constant, although thechlorophyll a/chlorophyll b ratio declined. When young tomato plants grown in low light were transferredto high light, the ATPase activity of isolated thylakoids increasedmarkedly within 1 d of transfer. This increase occurred morerapidly than changes in chlorophyll content per leaf area. Inaddition, in vivo chlorophyll fluorescence induction curvesindicate that forward electron transfer from Q^– occurredmore readily. The functional implications of these changes arediscussed. Key words: Tomato, leaves, light intensity, thylakoid membrane     

Ineffectiveness of cytokinin-induced chlorophyll retention in hypostomatous leaf discs

Kinetin retarded the decrease in chlorophyll content in leafdiscs from 5 species of plants with amphistomatous leaves, wherethe upper surface was exposed to air, but not in Rumex acetosera.When leaf discs were floated so that the lower surface was exposed,the effect of kinetin was less evident. Kinetin also stimulatedtranspiration in leaf discs from Nicotiana tabacum (amphistomatous),but not in leaf discs from Paederia chinensis (hypostomatous).Nor kinetin did retard chlorophyll breakdown in this specieswhen leaf discs were floated so that the stomatal surface wasin contact with the solution. The ineffectiveness of cytokininsin chlorophyll retention in leaf discs from hypostomatous leaveswas not due to reduced uptake of benzylaminopurine-¹⁴C. Chlorophyll retention was severely inhibited by coating theleaf surface with vaseline either in the presence or absenceof kinetin. Leaf discs floated on a solution exposed to CO₂-lessair retained more chlorophyll than those in normal air. Thereis thus a close relationship between stomatal opening (as measuredby stimulation of transpiration) and chlorophyll retention,as influenced by cytokinins. It is suggested that cytokinin-induced chlorophyll retentionand odier effects on leaf tissues could be mediated throughits effects on stomatal opening. (Received January 22, 1976; )     

Pigment Composition of a Novel Oxygenic Photosynthetic Prokaryote Containing Chlorophyll d as the Major Chlorophyll

The principal pigment found in the majority of oxygenic photosyntheticorganisms is known to be chlorophyll a. However, we isolateda new oxygenic photosynthetic prokaryote that contained chlorophylld as a predominant pigment with chlorophyll a being a minorpigment. Chlorophyll d had previously been noted but its naturaloccurrence and function remained unclear. Cells of the new prokaryotehad an absorption maximum at red region of 714–718 nmdue to chlorophyll d absorption, but no characteristic absorptionpeak of chlorophyll a around 680 nm was observed. Chlorophylld of the new organism was identified spectrophotometricallyin several solvents and its chemical structure was confirmedby NMR and FABMS analysis. The cell also contained a chlorophyllc-like pigment, zeaxanthin and a-carotene but not chlorophyllb and ß-carotene. The content of chlorophyll d accountedfor more than 2% of the cell dry weight, while the content ofchlorophyll a was less than 0.1%. The chlorophyll a/d ratioremained between 0.03 and 0.09 under different culture conditions.The light absorption characteristics and the high content ofchlorophyll d along with the small content of chlorophyll aindicated the existence of a new light utilization mechanisminvolving chlorophyll d. (Received October 7, 1996; Accepted December 16, 1996)     

Variation of Alkaloid Content in Erythroxylum coca Leaves from Leaf Bud to Leaf Drop

A sequential study describing the content (%) of alkaloids inleaves of Erythroxylum coca var. coca Lam. from leaf bud developmentto leaf drop has not previously been conducted. The length oftime the leaf resides on the plant and its concurrent metabolicactivity also has not been defined. In the present study, cocaine,methyl ecgonine, hygrine, tropinone, trans -cinnamoylcocaine,cis-cinnamoylcocaine, tropacocaine and cuscohygrine were monitoredto determine: (1) their content and patterns of accumulationfrom leaf bud to leaf drop; (2) the time leaves resided on theplant; and (3) whether leaves were metabolically active untilleaf drop. E. coca plants were grown in a controlled environmentfor 37 months. Leaves similar in chronological age were extractedand analysed for alkaloid content by gas chromatography (GC)and gas chromatography/mass spectrometry (GC/MS). Cocaine washighest in 7 d old rolled leaves (0·75%) and declinedto 0·39% at leaf drop. Cocaine, methyl ecgonine, hygrine,tropinone, trans -cinnamoylcocaine, cis-cinnamoylcocaine, cuscohygrineand tropacocaine content in 35 d old (mature) leaves was 0·61,0·59, 0·68, 0·08, 0·31, 0·55,0·52, and 0·05%. respectively. Cocaine, methylecgonine, hygrine, cis -cinnamoylcocaine, and cuscohygrine displayeda gradual decline from week 2 to week 36 of leaf duration. Tropinoneand tropacocaine were the least abundant of the alkaloids monitored.Cis-cinnamoylcocaine content exceeded cocaine at week 12, 16,and weeks 19 to 23 of leaf duration. Trans -cinnamoylcocainewas highest in rolled leaves (week 1) and in expanded leavesafter week 30. The monitored alkaloids appeared to be part ofthe metabolically active pool of the leaf. Leaves remained onthe E. coca plants for 36 weeks.Copyright 1994, 1999 AcademicPress Cocaine, methyl ecgonine, hygrine, tropinone, trans-cinnamoylcocaine, cis-cinnamoylcocaine, cusco-hygrine, tropacocaine, leaf bud, rolled leaves, expanded leaves, alkaloids, patterns, fluctuation, Erythroxylum coca var. coca, E, coca     

Estimation of the chlorophyll content of micropropagated potato plants using RGB based image analysis

A method has been developed for rapid and non invasive determination of chlorophyll content of leaves of micropropagated potato plants using RGB based image analysis. Among the trichomatic colors, R and G negatively correlated with the chlorophyll content, while a positive correlation was observed with B chromate. Compared to mean brightness value, the use of mean brightness ratio considerably improved the relationship of the tricolors with chlorophyll content. The brightness values and ratios of the primary colors are modeled as linear correlation functions for chlorophyll content. A significant correlation was observed between the model predicted chlorophyll content with the chlorophyll content measured by chlorophyll content meter. Spectral properties such as luminosity and saturation were also found to be negatively correlated with the chlorophyll content. The relationship was improved by combining the mean brightness ratio at B band region with luminosity. The potential of the imaging system in micropropagation has been discussed.     

The Effect of Nitrogen Fertilization and Irrigation Frequency on Photosynthesis of Potatoes (Solanum tuberosum)

Gas exchange parameters for the potato (Solanum tuberosum L.,cv. ‘Desiree’) crop were measured under field conditions.Nitrogen nutrition was found to have a positive effect on photosynthesisthroughout the growing season. The gas exchange data and thechlorophyll content in the leaves indicated that this effectwas essentially in the mesophyll. Stomatal resistance increasedas photosynthetic rate decreased, but substomatal CO₂ concentration(Ci) was not affected by nitrogen treatments. Long term effects of water deficit on photosynthetic capacitywere also mostly mesophyllic in origin. A reduction in photosyntheticrate was observed after a period of moisture stress and alsoafter relief of drought by irrigation, indicating a limitedcapacity for recovery. A short term afternoon increase in stomatalresistance, associated with lower Ci values, occurred afterlong periods without irrigation. Leaf water potential was affectedby irrigation frequency, but less strongly than the gas exchangeparameters. Mesophyll activity and stomatal behaviour were bothaffected by water stress and by nitrogen deficiency, whereasCi values were not affected in most cases. Solanum tuberosum L, photosynthesis, mesophyll, stomata, irrigation frequency, nitrogen deficiency, chlorophyll, leaf water potential     

Influence of Temperature on the Effects of Water Stress on Quercus Species

Quercus coccifera L. and Q. ilex L. leaves, collected in winter,when the plants were in full turgor, were treated with polyethyleneglycol (PEG) with a water potential of –48 and –65bar, at 15 °C and at 30 °C, for 2 days. The responseof each species differs with temperature as far as the plastidpigment, anthocyanin and soluble sugar content is concerned.Thus Q. ilex is affected more at 15 °C rather than at 30°C, while in Q. coccifera, apart from a small increase inanthocyanins, no significant change was observed at 15 °C.On the contrary, at 30 °C significant changes were observedin all studied parameters. Chloroplast pigments decreased generallyon the first day and their content either dropped further orincreased to reach the control values on the second day. Alltreatments resulted in an increase in anthocyanin content. Solublesugar content raised in Q. ilex at 15 °C and decreased inboth species at 30 °C. Quercus coccifera, Quercus ilex, oak, temperature, water stress, anthocyanin, chlorophyll, carotenoids     

Regulation of Leaf Senescence by Reproductive Sink Intensity in Cowpea (Vigna unguiculata L. Walp)

The relationship between seed number per pod and senescenceof the leaf in its axil was examined in a determinate cowpea(Vigna unguiculata L. Walp) variety C.779. The seed number perpod was reduced at all fruiting nodes by surgical excision ofpart of the 4-d-old pod. Leaf senescence as measured by lossof leaf area, chlorophyll content and soluble protein was sloweddown in leaves supporting the development of an artificiallyreduced number of seeds. Diminished nitrogen mobilization fromthe leaf could not account for the reduced rate of leaf senescence.The result suggests the involvement of a senescence signal fromthe developing seeds to the leaf in its axil. Development ofthe basal half of the excised pod in the cowpea provides a uniquesystem for manipulating seed number per pod. Senescence, monocarpic, chlorophyll, protein, Vigna unguiculata, cowpea     

Changes of Anatomical Features, Photosynthesis and Ribulose Bisphosphate Carboxylase-Oxygenase Content of Mango Leaves

Changes in anatomical and physiological features, includingchanges in amount per unit area of anthocyanin and chlorophyll,in leaves of seedling mango (Mangifera indica L. cv. Irwin)trees were determined to understand what controls the rate ofphotosynthesis (Pn) at various stages of development. The youngleaves of seedling trees contained high concentrations of anthocyanin.During enlargement of leaves, the disappearance of anthocyaninand the accumulation of chlorophyll occurred concomitantly;the anthocyanin content began to decrease markedly once theleaf area had reached a maximum. During the early period ofleaf development, the thickness of mesophyll tissue decreasedtemporarily, but when the length of the leaf reached half thatof a mature leaf, the mesophyll began to thicken again. Smallstarch grains appeared in the chloroplasts of the young leavesand chloroplast nucleoids (ct-nuclei) were distributed throughoutthe chloroplasts. When leaves matured, ct-nuclei were displacedto the periphery of chloroplasts because of the accumulationof large starch grains. Compared with young leaves, green andmature leaves contained greater concentrations of ribulose bisphosphatecarboxylase-oxygenase (RuBisCO) protein. The results of immunocytochemicalexamination of RuBisCO under the light microscope reflectedthe results of electrophoresis measurements of RuBisCO. Pn waslow during the chocolate-coloured stage of early leaf development.In green and mature leaves Pn was higher; the average Pn was7·6 mg CO₂ dm^-2 h^-1 under light at intensities above500 µmol m^-2 s^-1.Copyright 1995, 1999 Academic Press Mangifera indica L., mango leaf, chloroplast nucleoids, chloroplast ultrastructure, starch accumulation, anthocyanin, chlorophyll, DAPI staining, SDS-PAGE, immunocytochemical technique     

Effect of UV-B Radiation on Leaf Optical Properties Measured with Fibre Optics

Changes in the internal light microenvironment in leaves ofplants of Brassica campestris L. cv. Emma, B. carinata L., andMedicago saliva L. cv. Armour in response to exposure to UV-B(UV-B, 280–320 nm) radiation were measured using a fibreopticmicroprobe. Plants were exposed for 2 weeks either to high visiblelight or to supplemental ultraviolet-B radiation. The spectral regime (400–700 nm; PAR) was measured eithermidway through the leaf palisade or the spongy mesophyll. Afterexposure to UV-B radiation leaves of Brassica campesiris attenuatedtransmitted light more than the controls. At the same time bothforward and back scattered light increased in the palisade andspongy mesophylls. In contrast, UV-treatment of Medicago salivaleaves increased light transmission into the palisade, whilethe back scattered component showed little change. Leaves ofcariiwla showed little change in response to UV. Other responsesto UV-B radiation included increases in leaf thickness, decreasedtotal chlorophyll content, and changes in UV-B screening pigmentsand chlorophyll fluorescence induction kinetics. Brassica campestriswas most sensitive to exposure to enhanced levels of UV-B radiation,whereas leaves of B. carinata were the least sensitive. Ourdata indicate that exposure to UV-B radiation altered the lightmicroenvironment within leaves of the species different ways.These changes appeared to be caused by alterations in pigmentcontent and leaf anatomy. In turn, the altered distributionof PAR within the leaf could influence photosynthesis. Key words: Brassica campestris, Brassica carinata, fibre optics, light scattering, Medicago saliva, optical properties, ozone depletion, photosynthesis, ultraviolet radiation     

Light Dependency of Carboxylation Efficiency and Ribulose-1, 5-Bisphosphate Carboxylase Activation in Trifolium subterraneum L. Leaves

The effect of photosynthetic photon flux density (PPFD) on carboxylationefficiency, estimated as the initial slope (IS) of net CO₂ assimilationrate versus intercellular CO₂ partial pressure response curve,as well as on ribulose-1, 5-bisphosphate carboxylase (Rubisco)activation was measured in Trifolium subterraneum L. leavesunder field conditions. The relationship between IS and PPFDfits a logarithmic curve. Rubisco activation accounts for theIS increase only up to a PPFD of 550 µmol photons m^-2s^-1. Further IS increase, between 550 and 1000 µmol photonsm^-2 s^-1, could be related to a higher ribulose fcwphosphate(RuBP) availability. The slow, but sustained IS increase above1000 µmol photons m^-2 s^-1 could be explained by the mesophyllCO₂ diffusion barriers associated with the high chlorophylland protein content in field developed leaves. Key words: Photosynthesis, initial slope, ribulose-1, 5-bissphosphate carboxylase activation, light response, Trifolium subterraneum L     

A Preliminary Study on the Effects of Nitrogen Supply on the Growth In Vitro of Nine Potato Genotypes (Solanum spp)

Cultures of nine potato genotypes (seven Solanum tuberosum oneS. sparsipilum and one S. oplocense genotypes) were examinedfor their response to growing on medium containing either 60mol m^–3, 40 mol m^–3 or 20 mol m^–3 nitrogen.Genotypes differed in their response to nitrogen. Reducing thenitrogen regime tended to produce taller plants with longerinternodes, shoots had larger leaves but contained less chlorophyll.No change in fresh weight or number of nodes was observed. Genotypex nitrogen interactions were significant for chlorophyll content,shoot length and internode length. Results suggest that thechanges observed were as a result of changes in the total nitrogenlevel rather than changes in the ammonium : nitrate ratio. Thisstudy suggests that for certain potato genotypes, nitrogen levelsin MS medium are too high for producing desirable microplantsin terms of leaf area and shoot length Key words: Solanum tuberosum, S. sparsipilum, S. oplocense, micropropagation, morphogenesis