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1.
High-light damage in air-dry thalli of Lobaria
pulmonaria were measured in the laboratory as reductions in
maximal PSII efficiency (Fv/Fm)
after a 48 h recovery in a hydrated state at low light to account for
permanent damage. Thalli treated with the lowest light dose (90 mol photons
m-2) recovered normal
Fv/Fm-values with increasing irradiances (400-700 nm)
up to 1000 mol photons
m-2 s-1. Doubling this dose
lowered the threshold level for damage from 1000 to 320 mol photons m-2
s-1, and reduced
Fv/Fm at 1000 mol
photons m-2 s-1 by more than
50%. A second doubling of the dose to 360 mol photons
m-2 caused damage at 200 mol photons
m-2 s-1, and a nearly
complete cessation of PSII efficiency occurred at 1000 mol photons
m-2 s-1. No reciprocity of
irradiance and duration of illumination for PSII function was found. The
measured time-dependent decrease in
Fv/Fm was remarkably similar for
the naturally coupled, but artificially separated, light and temperature
factors. Therefore, the damage of high light on desiccated L.
pulmonaria seemed to be an additive effect of high irradiance
and high temperatures. Air-dry thalli were highly heat susceptible, being
affected already at temperatures around 40C.
Logging operations in forests are likely to raise the solar radiation at
remaining lichen sites to destructive levels.Keywords:
Lichens, high-light damage, heat stress, poikilohydric
organisms, reciprocity.
相似文献
2.
Photosynthetic activity of the calyx, green shoulder, pericarp, and locular parenchyma of tomato fruit 总被引:5,自引:1,他引:4
Photosynthesis of tomato fruit was studied using green fruit from six
heritage cultivars of Lycopersicon esculentum Mill.
and one of Lycopersicon pimpinellifolium. Chlorophyll
concentrations in the green shoulder, pericarp and locular parenchyma of
the fruit were determined and the apparent photosynthetic electron
transport activity (ETR) and chlorophyll fluorescence quenching
characteristics of these tissues and the calyx were compared. In all
cultivars, green shoulder formation, apparent as intense pigmentation of
the proximal pericarp shoulder, was positively related to the degree of
shading of the fruit during development. Appearing as a photosynthetic
adaptive trait for increasing the photoautotrophic capacity of fruit grown
under low light, the green shoulder contained 17-57% of the total pericarp
chlorophyll content. The pericarp below the green shoulder had lower
chlorophyll a+b. At a photon flux
density (PFD) of 1200 mol
m-2 s-1, different fruit
tissues were found to have different levels of ETR. In 'Yellow Pear', the
upper surface of the calyx had an ETR of 154 mol m-2
s-1, while the lower surface had an ETR of 88
mol m-2 s-1. On the
green shoulder, ETR was 203 mol m-2
s-1, whereas in the pericarp distal to the green
shoulder, ETR was 97 mol m-2
s-1. In the locular parenchyma, ETR was 66
mol m-2 s-1. This
trend towards a lower ETR in distal and internal fruit tissues appeared to
indicate a shift towards a more shade-type photosynthesis. Concomitant with
this shift were changes in chlorophyll fluorescence quenching
characteristics. Generally when tissues displayed reduced levels of ETR
they also displayed a faster decrease in the photochemical quenching
coefficient qp and a more rapid diversion of absorbed
photon energy to non-photosynthetic activity found in the calyx, green
shoulder, pericarp, and locular parenchyma suggest that all of these
tissues have significant roles in CO2 scavenging and the provision of
carbon assimilates. The potential role of fruit photosynthesis in
influencing the fruit acid to sugar ratio and hence fruit quality is
discussed. 相似文献
3.
Influence of UV-B radiation and Cd2+ on chlorophyll fluorescence, growth and nutrient content in Brassica napus 总被引:8,自引:0,他引:8
The possible interaction of two stresses, UV-B radiation and cadmium,
applied simultaneously, was investigated in Brassica
napus L. cv. Paroll with respect of chlorophyll fluorescence,
growth and uptake of selected elements. Plants were grown in nutrient
solution containing CdCl2, (0, 0.5, 2 or 5 M)
and irradiated with photosynthetically active radiation
(PAR, 400-700 nm, 800 mol m-2
s-1) with or without supplemental ultraviolet-B
radiation (UV-B, 280-320 nm, 15 kJ m-2
d-1, weighted irradiance). After 14 d of treatment,
the most pronounced effects were found at 2 and 5 M CdCl2 with and
without supplemental UV-B radiation. Exposure to cadmium significantly
increased the amount of Cd in both roots and shoots. In addition, increases
occurred in the concentrations of Fe, Zn, Cu, and P in roots, while K was
reduced. In shoots the S content rose significantly both in the presence
and absence of UV-B radiation, while significant increases in Mg, Ca, P,
Cu, and K occurred only in plants exposed to Cd and UV-B radiation.
Manganese decreased significantly under the combined exposure treatment.
The rise in S content may have been due to stimulated glutathione and
phytochelatin synthesis. Cadmium exposure significantly decreased root dry
weight, leaf area, total chlorophyll content, carotenoid content, and the
photochemical quantum yield of photosynthesis. As an estimation of energy
dissipation processes in photosynthesis, non-photochemical quenching
(qNPQ) was measured using a pulse amplitude modulated
fluorometer. The qNPQ increased with increasing Cd,
while the combination of cadmium and UV-B reduced the
qNPQ compared to that in plants exposed only to
cadmium or UV-B radiation. The chlorophyll a:b ratio
showed a reduction with UV-B at no or low Cd concentrations (0 M,
0.5 M CdCl2), but not at the higher Cd concentrations used (2
M, 5 M CdCl2). Thus in some instances there appeared to
be a UV-B and Cd interaction, while in other plants response could be
attributed to either treatment alone.Keywords:
Brassica napus, cadmium, ultraviolet-B
radiation.
相似文献
4.
The changes in photosynthetic activity and composition of pigments induced
by changes in temperature were examined in the third leaf of three
chilling-tolerant and three chilling-sensitive genotypes of maize
(Zea mays L.). The plants were grown under a
controlled environment at a photon flux density of 550 mol m-2
s-1, a 12 h photoperiod and at a suboptimal
temperature of 14/12 C (day/night) until the
full expansion of the third leaf. After this treatment, the
chilling-tolerant genotypes, when compared with the sensitive ones,
displayed a higher photosynthetic activity, a higher content of chlorophyll
(Chl) a+b, a higher Chl
a/b ratio, a larger total carotenoid pool size as well
as a different carotenoid composition. When temperature was subsequently
increased to 24/22 C for 3 d the composition
of the pigments changed, but the chilling-sensitive genotypes, while
adjusting their lower Chl a/b ratio and their
different carotenoid composition, were unable to adjust their lower content
of chlorophyll, their smaller total carotenoid pool size or their lower
photosynthetic performance. Moreover, while the chilling-tolerant genotypes
converted the most part of zeaxanthin to violaxanthin in the xanthophyll
cycle, the chilling-sensitive genotypes retained high amounts of
zeaxanthin. The changes in pigment composition that occurred over the 3 d
at 24/22 °C were largely conserved when the plants were returned to
14/12 °C, but photosynthetic activity decreased and zeaxanthin
accumulated again. The results suggest that the capability of the
chilling-tolerant genotypes, when compared with the sensitive ones, to
retain high amounts of pigments and to form a competent photosynthetic
apparatus at low temperature is the basis for their more vigorous growth in
cool climates. 相似文献
5.
Apical abortion in calabrese (Brassica oleracea var.
italica), a highly destructive disorder which occurs
in overwintered transplants, has been investigated using a model system in
which blindness (abortion of the apical meristem) can be reproducibly and
predictably induced. An initial experiment examined the susceptibility of
12 cultivars to apical abortion when grown throughout a winter period under
commercial conditions. Three of those varieties showed very high levels of
blindness (100%). Subsequently, plants of the susceptible cultivar PETO
7204 were subjected to an inductive period of low light intensity (30
mol m-2
s-1) and low temperature (4 C). Apical meristematic cells of all plants ceased
mitotic activity within 3 d of being transferred to a regime comprising
higher light intensity (100 mol
m-2 s-1) and temperature (15
C). Using this system the structures of
normal apices were compared with those which became blind. Blindness was
characterized by a cessation of leaf primordium production by the
vegetative apex, the last formed primordium growing on in some cases to
form a mature normal leaf, or in others, a deformed structure known as a
whip-tail. The inactive apical bud became embedded in the tissues of this
last-formed structure. The cells of the inactivated apical bud remained
alive, but lost their meristematic capability, becoming enlarged, highly
vacuolated parenchyma cells with amyloplasts.Keywords:
Apical abortion, apical meristem, blindness, calabrese.
相似文献
6.
The effect of rhizosphere dissolved inorganic carbon on gas exchange characteristics and growth rates of tomato seedlings 总被引:2,自引:0,他引:2
The possibility that an enhanced supply of dissolved inorganic carbon
(DIC=CO2+HCO3-) to the root solution could increase
the growth of Lycopersicon esculentum (L.) Mill. cv.
F144 was investigated under both saline and non-saline root medium
conditions. Tomato seedlings were grown in hydroponic culture with and
without NaCl and the root solution was aerated with CO2 concentrations in
the range between 0 and 5000 mol
mol-1. The biomass of both control and
salinity-stressed plants grown at high temperatures (daily maximum of
37C) and an irradiance of 1500 mol m-2
s-1 was increased by up to 200% by enriched
rhizosphere DIC. The growth rates of plants grown with irradiances of less
than 100 mol m-2 s-1
were increased by elevated rhizosphere DIC concentrations only when grown
at high shoot temperatures (35C) or with
salinity 28°C). At high light intensities, the photosynthetic rate,
the CO2 and light-saturated photosynthetic rate (jmax)
and the stomatal conductance of plants grown at high light intensity were
lower in plants supplied with enriched compared to ambient DIC. This was
interpreted as 'down-regulation' of the photosynthetic system in plants
supplied with elevated DIC. Labelled organic carbon in the xylem sap
derived from root DI14C incorporation was found to
be sufficient to deliver carbon to the shoot at rates equivalent to 1% and
10% of the photosynthetic rate of the plants supplied with ambient- and
enriched-DIC, respectively. It was concluded that organic carbon derived
from DIC incorporation and translocated in the xylem from the root to the
shoot may provide a source of carbon for the shoots, especially under
conditions where low stomatal conductance may be advantageous, such as
salinity stress, high shoot temperatures and high light
intensities. 相似文献
7.
Changes in components of leaf water potential during soil waterdeficits influence many physiological processes. Research resultsfocusing on these changes during desiccation of peanut (Arachishypogeae L.) leaves are apparently not available. The presentstudy was conducted to examine the relationships of leaf waterl, solute s and turgor p potentials, and percent relative watercontent (RWC) of peanut leaves during desiccation of detachedleaves and also during naturally occurring soil moisture deficitsin the field. The relationship of p to l and RWC was evaluated by calculatingp from differences in l and s determined by thermocouple psychrometryand by constructing pressure-volume (P-V) curves from the land RWC measurements. Turgor potentials of Early Bunchand Florunner leaves decreased to zero at l of1.2 to 1.3 MPa and RWC of 87%. There were no cultivardifferences in the l at which p became zero. P-V curves indicatedthat the error of measuring s after freezing due to dilutionof the cellular constituents was small but resulted in artefactualnegative p values. Random measurements on two dates of l, s, and calculation ofp from well-watered and water-stressed field plots consistingof several genotypes indicated that zero p occurred at l of1.6 MPa. It was concluded that the relationships of p,l, s, and RWC of peanut leaves were similar to leaves of othercrops and that these relationships conferred no unique droughtresistance mechanism to peanut. 相似文献
8.
Short communication. A steep Ca2[IMAGE]-dependence of a K[IMAGE] channel in a unicellular green alga
Bauer C; Plieth C; Hansen U; Simonis W; Schonknecht G 《Journal of experimental botany》1998,49(327):1761-1765
An increase of cytosolic Ca2 in the
unicellular green alga Eremosphaera viridis activities
Ca2-dependent
K channels causing a hyperpolarization of
the plasma membrane. Data from parallel calcium, and potential measurements
were combined with I/V relationships. This yielded a
steep Ca2-dependence of
K channels with a co-operativity of 4 and
an affinity of 300 nM.Key words: Eremosphaera viridis,
plasma membrane, Ca2-dependent
K channel, co-operative binding.
相似文献
9.
Characterization of the elicitor-induced biosynthesis and secretion of genistein from roots of Lupinus luteus L 总被引:2,自引:0,他引:2
Genistein is a multi-functional isoflavonoid naturally secreted from roots
of hydroponically grown legume plants. Roots of hydroponically cultivated
yellow lupin (Lupinus luteus L.) plants, transferred
into water secreted minor amounts of genistein (about 5 g g-1 fr. wt.). Secretion of
genistein from L. luteus roots (rhizosecretion) was
stimulated dramatically to over 100 g
g-1 root fresh weight by soluble chitosan, salicylic
acid (SA) and potassium cyanide (KCN) supplied at 0.12% (w/v), 800
M and 400 M, respectively. Other identified elicitors
caused a smaller induction of genistein rhizosecretion. Increased levels of
genistein in root exudates corresponded to greater amounts of genistein in
root tissue. Elicitor-induced rhizosecretion of genistein was based on
de novo synthesis and was inhibited by glyphosate and
other less specific metabolic inhibitors. Except for NaF:AICI3, all tested
elicitors of genistein rhizosecretion produced a distinct bell-shaped
dose-response curve. Most of the elicitor-induced rhizosecretion of
genistein occurred during the first day, followed by a gradual decline.
Further addition of elicitor treatments had little effect of genistein
rhizosecretion, indicating that the induction of genistein rhizosecretion
by the identified elicitors is a once only event.Keywords:
Genistein, isoflavonoids, Lupinus luteus,
elicitation, exudation.
相似文献
10.
Mastoparan analogues stimulate phospholipase C- and phospholipase D-activity in Chlamydomonas: a comparative study 总被引:1,自引:0,他引:1
van Himbergen J; ter Riet B; Meijer H; van den Ende H; Musgrave A; Munnik T 《Journal of experimental botany》1999,50(341):1735-1742
The G-protein activator mastoparan and its analogues are becoming popular
tools for studying signalling in plants. Therefore the abilities of
mastoparan, mas7, mas8, and mas17 to activate phospholipase C (PLC), PLD
and to induce the deflagellation response in Chlamydomonas
moewusii Gerloff were compared. The aim was to test whether
their relative potencies in a plant system resemble those reported for
bovine brain Go and Gi, as is generally assumed, and to determine at which
concentrations cells become permeabilized, a known effect of higher
concentrations. The concentrations at which 50% deflagellation was induced,
were 2.0 M mastoparan, 3.0 M mas8, 3.6 M mas7, and 5.8 M
mas17. Similar activities were found for the production of phosphatidic
acid, which is the result of the combined activities of PLD and PLC
(together with diacylglycerol kinase). PLD activity alone was measured
in vivo by its ability to phosphatidylate
n-butanol. Surprisingly, the concentrations that
stimulated maximum activity were about 10-fold lower (1
M) than those that stimulated maximum PLC activity (10
M). Mas17 was an exception with both maxima above 10 M.
All the compounds except mas17 permeabilized C.
moewusii cells. The concentrations at which 50% of the cells
were permeabilized to Evan's blue were 7.4 M mas8, 16.0 M
mas7 and 22.4 M mastoparan. In conclusion, only mastoparan itself
and the least active analogue mas17 induced maximum deflagellation, PLC and
PLD activities without permeabilizing the cells.Keywords:
Chlamydomonas, deflagellation, mastoparan,
phospholipases C and D, phospholipid metabolism
相似文献
11.
Natural abundance of 15N in amino acids and polyamines from leguminous nodules: unique 15N enrichment in homospermidine 总被引:2,自引:0,他引:2
The natural 15N abundance
(15N value) in acetylpropyl derivatives of
amino acids and in ethyloxycarbonyl derivatives of polyamines was
determined using a gas chromatography/combustion/mass
spectrometer-(GC/C/MS). 15N value
determined for 12 amino acids and five polyamines by GC/C/MS were identical
to those obtained by a direct combustion method using an automatic nitrogen
and carbon analysis (ANCA) mass spectrometer, the difference being less
than 1.0% in most cases. The GC/C/MS
method was used to analyse 15N values in
the amino acids and polyamines from root nodules of pea and faba bean and
from stem nodules of Sesbania rostrata. The analysis
of 15N values revealed that homospermidine
had high 15N values, as much as +40%, while
the amino acids investigated had 15N values
between -3 and +6%, putrescine between +2 and +8%, cadaverine between +1
and +7%, spermidine between -2 and +4%, and spermine between 0 and +6%. The
mechanism of 15N enrichment in homospermidine is
discussed. 相似文献
12.
Leaf diffusion resistance interpreted as stomatal resistance,leaf water potential (w), solute potential (s) and leaf turgorpotential (p) of the chilling sensitive species Phaseolus vulgariswere determined during chilling at 4 °C in the light. Bothchill-hardened and non-hardened plants were used. For comparison,the chilling resistant species Pisum sativum was also used. The results for chilled P. sativum were similar to those obtainedfor chill-hardened P. vulgaris plants receiving a chilling treatment.In both cases a reduction in stomatal aperture and the maintenanceof a positive leaf turgor were the responses to chilling. Leavesof chilled but non-hardened P. vulgaris plants were found tomaintain open stomata throughout the chilling treatment despitea severe wilt developing after 7 h at 4 °C. This was incontrast to the chill-resistant P. sativum. which showed a rapidclosing and subsequent re-opening of the stomata to a new reducedaperture. During the first 12 h of chilling wof P. vulgaris leaves changedfrom 0.47 MPa to 1.24 MPa. On more prolonged chillingw tended to return to pre-chilling values. In addition. p decreasedfrom 0.42 MPa to zero after only 9 h of chilling, and remainedat this value for the remainder of the chilling period, s, changedrapidly from 0.89 MPa to 1.35 MPa in the first7.5 h, and after 9 h. w and s, were equal, i.e. zero p. In contrast,the chilling resistant plant P. sativum maintained a positivep throughout the chilling period, and there was little differencebetween values of w, and s in control and chilled leaves. Key words: Chilling, Stomata, ater relations, Phaseolus vulgaris, Pisum sativum 相似文献
13.
Thomas, H. 1987. Physiological responses to drought of Loliumperenne L.: Measurement of, and genetic variation in, waterpotential, solute potential, elasticity and cell hydration.J.exp. Bot. 38: 115125. Clonally-replicated genotypes of Loiium perenne L. were grownin a controlled environment. Leaf water potential (w) osmoticpotential (s), turgor potential (p = w s), elasticity(E), leaf hydration (g water per g dry matter, H) and numberof green leaves per tiller (NGL) were measured before and duringa 42 d drought treatment. A simplified method of estimating E (at w < 1?0 MPa) usingonly six measurements was developed to permit a measurementrate of 8 leaves per hour. Measurement errors in all characterswere 3% or less. During drought, w and s (at w = 0?5 MPa) decreased significantly,p and E increased significantly, and H decreased slightly. Plantsize during drought was negatively correlated with s, and Hand positively correlated with p, osmotic adjustment, E andNGL. Measurements made on the genotypes before draughting didnot give a reliable indication of their physiological conditionafter adaptation to drought. Genetically controlled variation (broad sense heritability)of drought-adapted plants for E was 15%, w 23%, s, 34%, p, 35%,H 34% and NGL 64%. The possibilities for, and effectivenessof, divergent selection of genotypes with high and low expressionof the characters are discussed. Key words: Water relations, Lolium, genetic variation 相似文献
14.
The Meaning of Matric Potential 总被引:6,自引:1,他引:5
The commonly used equation, = P - + , which describes thepartitioning of plant water potential, , into components ofhydrostatic pressure, P, osmotic pressure, , and matric potential,, is misleading. The term , which is supposed to show the influenceof a solid phase on , is zero if a consistent definition ofpressure is used in the standard thermodynamic derivation. However,it can be usefully defined by = + D, where D is the osmoticpressure of the equilibrium dialysate of the system. The practicaland theoretical significance of this definition is discussed. 相似文献
15.
The objective was to determine whether the protein of
rolB affects shoot formation and whether this
potential relationship depends on the developmental stages of the plant
and/or on the culture conditions. Thin cell layers (TCL) and leaf explants
were excised from tobacco plants in the vegetative and flowering stages and
cultured under various hormonal conditions. In TCLs of vegetative-stage
plants, the expression of rolB enhanced the formation
of the shoot buds under hormone-free conditions and with specific
concentrations of auxin and/or cytokinin. Histological examination showed
that the induction of the shoot meristemoids was particularly enhanced by
rolB protein and that meristemoid growth was
accelerated. In leaf explants from vegetative-stage plants, the expression
of rolB increased the formation of shoot buds in the
presence of 1 M IAA plus 1 or 10 M cytokinin. With BA alone, at a 0.1 M concentration, shoot formation occurred in the
transgenic explants only, whereas with concentrations ranging from 0.5 to
10 M, it was higher in these explants than in
controls.RolB protein enhanced the formation of shoot
buds in TCLs from flowering plants under all hormonal conditions. In the
presence of 1 M IAA and kinetin, the protein also increased the
flowering response. In leaf explants from flowering plants, the expression
of rolB increased the number of shoot buds in the
presence of 1 M IAA with 10 M BA.In conclusion,
rolB protein promotes shoot formation; it seems to
have a positive interaction with cytokinin and an effect on the induction
of the meristematic condition. 相似文献
16.
HENSON I. E.; ALAGARSWAMY G.; MAHALAKSHMI V.; BIDINGER F. R. 《Journal of experimental botany》1983,34(4):442-450
The water potential () at which stomata completed closure (8Lmin)was determined for pearl millet (Pennisetum americanum [L.]Leeke) at two growth stages by monitoring changes in leaf conductance(gL) and following shoot detachment. Leaf water status wasevaluated concurrently using a pressure-volume (P-V) technique. In a pot experiment with young vegetative plants, 8Lmin closelyapproximated to the estimated at zero turgor (u) both for controland for drought-conditioned plants which had osmotically adjusted.However, for penultimate leaves of field-grown flowering plants,8Lmin was found to be 0.61 (irrigated plants) and 0.87 (droughtedplants) MPa below u. In drought-stressed field-grown plants,osmotic adjustment (characterized by a decrease in solute (osmotic)potential (s ) at both full hydration and zero turgor) was insufficientto maintain a positive bulk leaf turgor potential (p) once had declined to below about -1.5 MPa. It is suggested that localizedadjustment by the stomatal complex in response to environmentaldifferences, leaf ageing and/or ontogenetic change, is responsiblefor the uncoupling of stomatal from bulk leaf water status. Key words: Stomata, Water stress, Pennisetum americanum 相似文献
17.
An improved strain-gauge device for continuous field measurement of stem and fruit diameter 总被引:7,自引:2,他引:5
An improved strain-gauge dendrometer was tested on apple (Pyrus
malus L.) tree trunks and fruit to measure thickness dynamics.
The sensor is similar to previous devices, but is more flexible allowing
for a greater range of thickness change before it has to be physically
reset. The practical resolution of the measurement system is given as one
standard deviation about the mean of 51 observations taken on an Invar
metal alloy in the field when temperatures ranged between 16C and 17C. The mean
of these observations was 3.68356 mm with one standard deviation of 0.00947
mm. There is a positive correlation between temperature and sensor output
having a slope of 2.96 m°C-1. For a typical
daily temperature change of 21°C, this causes an apparent change of
62 m. Stem thickness varied 0.7 mm diurnally
with maximum values at night and minimum values during the day. Apple fruit
diameter increased 3.3 mm over the 15 d period.Keywords:
Strain gauge dendrometer, plant stem and fruit thickness sensor,
plant water status, growth.
相似文献
18.
An error occurs in the calibration of xylem pressure potential() against leaf-water potential () when the calibration is madeusing plant material in which the water stress has been inducedartificially after excision. The impostion of water stress afterexcision affects the determination more than it affects , consequentlythe relationship between these two indices of water stress isaltered. Care should be exercised to ensure that identical proceduresare adopted during . calibrations and during susbsequent fieldmeasurements of with the pressure-chamber apparatus. 相似文献
19.
In a companion paper several methods of calculating the marginal unit water
cost of plant carbon gain (E/A) were tested to determine
whether stomata were behaving optimally in relation to regulating leaf gas
exchange. In this paper one method is applied to several tropical tree
species when leaf-to-air vapour pressure difference (D), photosynthetic
photon flux density, leaf temperature, and atmospheric soil water
availability were manipulated. The response of leaves that had expanded
during the dry season were also compared to that of leaves that had
expanded in the wet season. Few differences in absolute value of
E/A, or the form of the relationship, were observed
between species or between seasons. In the majority of species,
E/A increased significantly as either leaf-to-air vapour
pressure difference increased, at a leaf temperature of either 33C or 38C, or as in
photosynthetic photon flux density increased. In contrast, as leaf
temperature increased at constant D, E/A was generally
constant. As pre-dawn water potential declined, E/A
declined. The relationship between E/A and D did not
differ whether internal or ambient carbon dioxide concentration were kept
constant. It is concluded that stomata are only behaving optimally over a
very small range of D. If a larger range of D is used, to incorporate
values that more closely reflect those experienced by tropical trees in a
savanna environment optimization is incomplete.Key
words: Stomatal optimization theory, marginal unit water cost.
相似文献
20.
A reproducible system for somatic embryogenesis and plantlet formation of
sandalwood has been developed. A high frequency (100%) of somatic embryos
were induced directly from various explants in MS (Murashige and Skoog,
1962) medium with thidiazuron (1 or 2 M) or
indirectly in medium containing 2,4-D plus thidiazuron. Within 8 weeks,
white globular somatic embryos or friable embryogenic tissue developed on
cultured explants. In S. album the globular somatic
embryos were transferred to MS medium supplemented with IAA (6 M) and kinetin (1 and M) where they
developed further, multiplied and maintained friable embryogenic tissue.
After 15-30 d, mature somatic embryos (1-2 mm) with well-developed
cotyledons were separated and subcultured on to medium containing GA3 (6
M) for germination. Once germinated, elongated somatic embryos
(10-20 mm long) grew further in MS supplemented with lower GA3 (3
M). In S. spicatum, the addition of casein
hydrolysate and coconut milk was necessary for plantlet development from
somatic embryos. From histological studies, it appeared that primary
somatic embryos arose from single cells or had a multicellular origin from
the epidermis or cortical parenchyma. Secondary somatic embryos and friable
embryogenic tissue differentiated from groups of proembryogenic cells from
a superficial layer of the primary somatic embryos.Keywords:
Santalum album, Santalum spicatum, somatic
embryogenesis, histological studies.
相似文献