Gymnosperm Ginkgo Research Articles

Stomatal responses of the 'living fossil' Ginkgo biloba L. to changes in atmospheric CO2 concentrations

it occurs, on leaf gas exchange remains to be determined for temperate deciduous trees growing at CO 2 concentraLeaf stomatal density and index of Ginkgo biloba L. tions above present, although two previous studies have were both significantly (P<0.05) reduced after 3 years indicated the potential for such eVects. Woodward and growth at elevated CO 2 (560 ppm), with values com- Bazzaz (1988) noted correlations between stomatal denparable to those of cuticles prepared from Triassic sity and net photosynthesis and stomatal conductance and Jurassic fossil Ginkgo leaves thought to have ( g s ) for tree and shrub species growing at CO 2 concentradeveloped in the high CO 2 ‘greenhouse world’ of the tions between 225 and 340 ppm, whilst Berryman et al. Mesozoic. A reciprocal transfer experiment indicated (1994) reported that at 700 ppm CO 2 the tropical trees that reductions in stomatal density and index irrevers- Maranthes corymbosa and Eucalyptus tetrodonta showed ibly reduced stomatal conductance, particularly at low an irreversible reduction in maximum g s , as a consequence leaf-to-air vapour pressure deficits and low internal of lower stomatal densities. The results reported here are leaf CO 2 concentrations (C i ). These effects probably from a 3 year CO 2 enrichment (560 ppm) experiment contributed to the high water-use efficiency of Ginkgo investigating the stomatal and gas exchange responses of spp. in the Mesozoic relative to those of the present, the gymnosperm Ginkgo biloba L., an ancient taxon as determined from carbon isotope measurements of described by Darwin as a ‘living fossil’ and now widely extant and fossil cuticles. planted as an ornamental species in municipal gardens ( Tralau, 1968). Experimental results are compared with

Light-Regulated and Organ-Specific Expression of Types 1, 2, and 3 Light-Harvesting Complex b mRNAs in Ginkgo biloba

In a prior study (E. Chinn and J. Silverthorne [1993] Plant Physiol 103: 727-732) we showed that the gymnosperm Ginkgo biloba was completely dependent on light for chlorophyll synthesis and chloroplast development and that expression of light-harvesting complex b (Lhcb) mRNAs was substantially increased by light. However, dark-grown seedlings that were transferred to constant white light took significantly longer than angiosperm seedlings to initiate a program of photomorphogenesis and the stems failed to green completely. We have prepared type-specific probes for mRNAs encoding major polypeptides of light-harvesting complex II (Lhcb1, Lhcb2, and Lhcb3) and have used these to analyze the expression of individual Lhcb mRNAs during greening. All three sequences accumulated in the top portions of dark-grown seedlings transferred to light, but, as was seen previously for total Lhcb mRNAs, there was a transient, reproducible decline in the levels of all three mRNAs after 4 d in the light. This transient decrease in Lhcb mRNA levels was not paralleled by a decrease in Chl accumulation. By contrast, there were significantly lower levels of all three Lhcb mRNAs in the lower portions of greening dark-grown stems as well as lower Chl levels. We conclude that although the tops of the plants have the capacity to etiolate and green, Gingko seedling stems continue a program of development into woody tissue in darkness that precludes greening when the seedlings are transferred to the light.

Chloroplastic genomes of Ginkgo biloba and Chlamydomonas moewusii contain a chlB gene encoding one subunit of a light-independent protochlorophyllide reductase

We have cloned and sequenced a Chlamydomonas moewusii chloroplastic DNA fragment that includes a 563 amino-acid open reading frame (ORF563, chlB) presenting 89% amino-acid homology with ORF513 from Marchantia polymorpha. It is also homologous to ORF510 from Pinus thunbergii but includes two insertions absent in both M. polymorphia and P. thunbergii. The derived polypeptide is 54% similar to the product of bchB from Rhodobacter capsulatus, identified as one subunit of a light-independent NADH-protochlorophyllide reductase. We also isolated and sequenced an homologous chloroplastic gene from the gymnosperm Ginkgo biloba. Northern hybridizations performed on RNA isolated from synchronized Chlamydomonas eugametos cells showed higher expression between the tenth hour of light and the eighth hour of darkness, peaking during the first 2 h of darkness.

Light-Dependent Chloroplast Development and Expression of a Light-Harvesting Chlorophyll a/b-Binding Protein Gene in the Gymnosperm Ginkgo biloba

Unlike conifers, the gymnosperm Ginkgo biloba is dependent on light for chlorophyll (Chl) synthesis and initiation of chloroplast development. Dark-grown seedlings show complete etiolation, including no detectable Chl accumulation, no leaf expansion, and increased hypocotyl elongation. When dark-grown seedlings are placed in white light, Chl synthesis and leaf expansion are initiated, but unlike angiosperms, which initiate rapid photomorphogenesis, Ginkgo takes at least 1 week to change to a normal light-regulated pattern of growth. A cDNA clone (pLhcb*Gb1) encoding a Chl a/b-binding protein of light-harvesting complex II from Ginkgo mRNA has been used as a probe for the expression of this family of mRNAs. We have found that, in common with angiosperms but in marked contrast to pines, Lhcb mRNA is expressed in a highly light-dependent manner. In addition to being expressed in light-grown leaves, this sequence is also expressed in the green tissues of immature seeds. The Lhcb mRNA appears during greening in parallel with the onset of Chl synthesis. The complete sequence of pLhcb*Gb1 has been determined and the deduced amino acid sequence was found to be of type I based on comparison with signature sequences of angiosperm and gymnosperm sequences.

The N-terminal amino acid sequence of the β-subunit of the legumin-like protein from seeds of Ginkgo biloba

The sequence of the first 52 amino acids at the N-terminus of the β-subunit of a legumin-like protein from seeds of the gymnosperm Ginkgo biloba were determined by automated sequencing and DABITC/PITC micro-sequence analyses of peptides derived from the protein by enzymatic digestions and chemical cleavage with CNBr. The protein from Ginkgo exhibits sequence homologies (32–49% identities) with the 11S globulins and legume-like proteins from seeds of various angiosperm monocotyledons and dicotyledons.

Conservation of chloroplast genome structure among vascular plants

We have constructed the first physical map of a gymnosperm chloroplast genome and compared its organization with those of a fern and several angiosperms by heterologous filter hybridization. The chloroplast genome of the gymnosperm Ginkgo biloba consists of a 158 kb circular chromosome that contains a ribosomal RNA-encoding inverted repeat approximately 17 kb in size. Gene mapping experiments demonstrate a remarkable similarity in the linear order and absolute positions of the ribosomal RNA genes and of 17 protein genes in the cpDNAs of Ginkgo biloba, the fern Osmunda cinnamomea and the angiosperm Spinacia oleracea. Moreover, filter hybridizations using as probes cloned fragments that cover the entirety of the angiosperm chloroplast genome reveal a virtually colinear arrangement of homologous sequence elements in these genomes representing three divisions of vascular plants that diverged some 200–400 million years ago. The only major difference in chloroplast genome structure among these vascular plants involves the size of the rRNA-encoding inverted repeat, which is only 10 kb in Osmunda, 17 kb in Ginkgo, and about 25 kb in most angiosperms. This size variation appears to be the result of spreading of the repeat through previously single copy sequences, or the reverse process of shrinkage, unaccompanied by any overall change in genome complexity.

Hexitols in coconut milk: Their role in nurture of dividing cells

Coconut milk, the liquid endosperm of the coconut (Cocos nucifera L.), has special interest because it will induce otherwise mature, non-growing cells to divide and to grow rapidly (3, 4). Similar properties reside in analogous morphological situations, such as the immature caryopsis of Zea mays and the liquid present in immature fruits of Juglans (18) or of Aesf alus (12, 24, & also see 25). A nutritive relationship also exists between the female gametophyte, sometimes called endosperm, and the archegonia and embryos of the gymnosperm Ginkgo; extracts of this gametophyte will also induce cells of mature tissue of carrot root to resume active growth (18). Therefore, the fluids that nourish immature embryos seem especially able to induce growth in the mature cells even of some other plants than the ones in which they were laid down. This raises the question whether the behavior of the zygote is due to its special nature or to its nurture by the special fluid contents of the embryo sac, by the substances which are contained in the endosperm, and by other special nutritive organs. Free cells obtained from mature carrot phloem may be cultured in media which contain coconut milk (21) and may grow and regenerate a complete and mature plant (20). In this7 respect the free cells imitate the zygote, and the coconut milk its normal nutritional supply. Moreover, as the cells grow and develop, they form structures which are strongly reminiscent of pro-embryonic development (15). Therefore, a full knowledge of the chemical constituents of coconut milk which cause these growth responses would have an important bearing upon many problems of cell growth and cell division. This knowledge would also have important implications for protein synthesis, which is stimulated in quantity and modified in kind during the induction of growth in carrot and potato cells (27). Following the observations of Blakeslee and van Overbeek (28, 29), work upon the chemical constituents of coconut milk was pursued sporadically in different laboratories (for references see 25). In this laboratory, investigation has been in progress for some years. Clearly, the growth induction which is pr,oduced by the coconut milk, over and above the effects due to common nutrients and vitamins, is not a simple effect due to a single substance. On the contrary, it has been emphasized that no substance singly and independently controls cell division (see 25 & references there cited). In part the effect of coconut milk is non-specific and is replaceable by casein hydrolysate, or by other sources of the reduced nitrogen compounds, from which the cells may synthesize protein more readily than they do from nitrate (13). Even whole coconut milk alone will not trigger the growth of some cells (e.g. potato tuber), for it needs to be supplemented by one of a large array of compounds which are now known to act synergistically with the coconut milk. The substance 2,4-dichlorophenoxyacetic acid (2,4-D), and many of its analogues with different ring configurations or different side chains, can also function in this manner (14,16, see also 25). Several of the halogen-substituted phenylacetic acids (26) and certain a-substituted propionic acids (14) can also work along with the coconut milk. This paper now designates certain hexitols to be responsible for part of the effect for which coconut milk (or its morphological equivalent) has hitherto been regarded as a specific source. Early work on the chemical fractionation of coconut milk and similar fluids recently has been reviewed (25). This work encountered the difficulty that, when purified, the isolated substances only expressed their activity in the presence of other sub-fractions from the coconut milk. While this statement still holds true, the work to be described permits the critical identification of at least three of the synergists which contribute to the total growth which is stimulated by whole coconut milk.