Seed Production, Seed Populations in Soil, and Seedling Production After Fire for Two Congeneric Pairs of Sprouting and Nonsprouting Chaparal Shrubs

A study of seed production, seed storage in the soil, and seedling production after fire was undertaken for a sprouting and a nonsprouting congenerica pair of species of Ceanothus and Arctostaphylos. All species exhibited large fluctuations in annual seed production. There was a significant correlation between fruit production and precipitation in the previous year. It is hypothesized that high carbon gain in years of high precipitation results in high numbers of floral primordia which, in these species, remain dominant until the following year. It was also noted that high fruit production was not dependent upon high precipitation the same year; suggesting that the fruits were utilizing carbon stored from the previous year. All 4 species were capable of producing more seeds in a single season than were stored in the soil. Apparently the soil seed pools do not represent a steady accumulation of seeds in the soil but rather are the result of dynamic fluctuations in seed inputs and outputs. Each species also had more seeds in the soil, by several orders of magnitude, than seedlings after fire in an adjacent burned stand. The sprouting and seeding productive strategies are quite different in the two genera. The information from this study coupled with that from other studies indicate 4 reproductive modes: sprouting and seedling production (C. leucodermis), abundant seedling production (C. greggii), low seedling production but better “equipped” seedlings (A. glauca), and predominantly sprouting (A. glandulosa). [1]

 

High Frequencies of Fertilization and Haploid Seedling Production in Crosses Between Commercial Hexaploid Wheat Varieties and Maize

 

Nineteen commercial hexaploid wheat varieties were crossed with the maize F1 hybrid ‘Seneca 60’. Fertilization frequencies ranged from 32.1 % to 47.5 % of pollinated florets (mean 39.5 %) in the 14 winter wheat varieties and from 40.7 % to 51.4 % (mean 47.8 %) in the five spring wheat varieties. In some cases only an endosperm was formed and the frequencies of embryo formation were therefore slightly lower, being 28.2 % to 45.9 % (mean 36.4 %) for winter wheats and 39.8 % to 48.6 % (mean 45.1 %) for spring wheats. Mean values were significantly higher in the spring wheats but no significant variation was found between varieties within the spring or winter categories. In the five spring wheats the mean yield of embryos, and hence the potential yield of haploid plants, was 3.4‐fold higher than with the tetraploid Hordeum bulbosum clone PB179. For the 14 winter wheats the figure was 10.9‐fold higher. These differences were highly significant (p < 0.001) in all varieties. A single 2,4‐D treatment given to spikes one day after pollination with maize enabled embryos to be recovered from all 19 varieties. A total of 311 embryos were recovered from 950 florets (an average of 7.3 embryos per spike) of which 191 germinated, giving an average yield of one haploid plant for every 5.0 florets pollinated (4.4 haploid plants per spike).[2]

 

Enhancement of American chestnut somatic seedling production

Somatic embryogenesis holds promise for mass propagation of American chestnut trees bred or genetically engineered for resistance to chestnut blight. However, low germination frequency of chestnut somatic embryos has limited somatic seedling production for this forest tree. We tested the effects of culture regime (semi-solid versus liquid), cold treatment, AC and somatic embryo morphology (i.e., cotyledon number) on germination and conversion of the somatic embryos. Cold treatment for 12 weeks was critical for conversion of chestnut somatic embryos to somatic seedlings, raising conversion frequencies for one line to 47%, compared to 7% with no cold treatment. AC improved germination and conversion frequency for one line to 77% and 59%, respectively, and kept roots from darkening. For two lines that produced embryos with one, two or three-plus cotyledons, cotyledon number did not affect germination or conversion frequency. We also established embryogenic American chestnut suspension cultures and adapted a fractionation/plating system that allowed us to produce populations of relatively synchronous somatic embryos for multiple lines. Embryos derived from suspension cultures of two lines tested had higher conversion frequencies (46% and 48%) than those from cultures maintained on semi-solid medium (7% and 30%). The improvements in manipulation of American chestnut embryogenic cultures described in this study have allowed over a 100-fold increase in somatic seedling production efficiency over what we reported previously and thus constitute a substantial advance toward the application of somatic embryogenesis for mass clonal propagation of the tree.[3]

 

Effect of Gamma Rays on Seed Germination, Seedling Height, Survival Percentage and Tiller Production in Some Rice Varieties Cultivated in Sierra Leone

Thirteen rice varieties cultivated in Sierra Leone were used to examine varietal differences in radiosensitivity to gamma radiation during the wet season of 2006 in the lowland ecology. Dry seeds of rice varieties were exposed to gamma radiation ranging from 50 to 800 Gy to determine their responses to radiation and the effective radiation dose for mutation breeding. Percentage germination, percentage survival (field condition), seedling height and tiller production were the traits measured on the M1 generation. The results indicated that increasing doses of gamma irradiation had no effect on germination for the first seven days under laboratory conditions. Percentage survival of germinated seedlings from the 8th to 14th day under laboratory conditions decreased significantly with increase in radiation dose up to 600 Gy. With increase in radiation above 300 Gy a reduction in seedling height and percentage survival under field conditions was observed in irradiated plants of M1 generation. Increase in gamma ray doses from 50 to 300 Gy had little or no effect on tiller production as there were no significant differences in tiller number of irradiated seeds and non-irradiated (control) for all the varieties evaluated. The LD50 values determined from regression analysis based on percentage field survival ranged from 345 Gy for ROK18 to 423 Gy for ROK22. These ranges of LD50 values determined for the different rice varieties could be useful in rice varietal improvement programmes in Sierra Leone.[4]

 

Effects of Iron Ions on Rosmarinic Acid Production and Antioxidant System in Melissa officinalis L. Seedlings

Aims: In this study, effects of various Fe2+ concentrations on the physico-chemical parameters including contents of rosmarinic acid, flavonoid and anthocyanin as well as antioxidant enzymes activity in Melissa officinalis seedlings were analyzed. Furthermore, some morphological parameters and contents of chlorophyll and carotenoid were investigated in 45-day-old M. officinalis seedlings in presence of various Fe2+ concentrations.

Study Design: completely random designs.

Place and Duration of Study: Department of Biotechnology, Institute of Science and High technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran.

Methodology: 45-day-old seedlings were treated with different Fe2+ concentrations and then physico-chemical parameters of them were evaluated after 8 and 16 hours incubation periods. Rosmarinic acid content was measured using HPLC and the flavonoid and anthocyanin contents were determined using a spectrophotometer. Morphological properties including seed germination, root and shoot elongation and dry biomass of the 45-day-old Fe2+-treated seedlings were analyzed.

Results: The results showed that the contents of rosmarinic acid, flavonoid and anthocyanin drastically decreased in all treatments compared to the control. In this condition, the activity of superoxide dismutase and peroxidase were increased more significantly after 8 hours treatment rather than 16 hours. The results revealed that changes in rate of germination, shoot elongation and dray biomass were not statically significant. Although, the root growth was decreased in presence of Fe2+ compared to control, that was significant at the level of 5% at the highest Fe2+ concentration.

Conclusion: Accumulation of free radicals under treatment conditions may lead to suppression of protein synthesis or degradation of them as indirectly confirmed by reduced protein content. Therefore, it may be concluded that the decrease in contents of rosmarinic acid, flavonoid and anthocyanin results from a reduction of enzyme levels in their biosynthesis pathways. The decrease in root growth can be due to exposition of the organ to the excess of Fe2+, more increased uptake of the ion and triggering of free radicals. Furthermore, low rate in Fe2+ transportation to the shoots and elevated levels of chlorophyll and carotenoid contents may have roles in preventing damages to this organ.[5]

 

 

Reference :

[1] Keeley, J.E., 1977. Seed production, seed populations in soil, and seedling production after fire for two congeneric pairs of sprouting and nonsprouting chaparal shrubs. Ecology, 58(4), pp.820-829.

[2] Laurie, D.A. and Reymondie, S., 1991. High frequencies of fertilization and haploid seedling production in crosses between commercial hexaploid wheat varieties and maize. Plant Breeding, 106(3), pp.182-189.

[3] Andrade, G.M. and Merkle, S.A., 2005. Enhancement of American chestnut somatic seedling production. Plant Cell Reports, 24(6), pp.326-334.

[4] Harding, S. S., Johnson, S. D., Taylor, D. R., Dixon, C. A. and Turay, M. Y. (2012) “Effect of Gamma Rays on Seed Germination, Seedling Height, Survival Percentage and Tiller Production in Some Rice Varieties Cultivated in Sierra Leone”, Journal of Experimental Agriculture International, 2(2), pp. 247-255. doi: 10.9734/AJEA/2012/820.

[5] Esmaeilzadeh-Salestani, K. and Riahi-Madvar, A. (2014) “Effects of Iron Ions on Rosmarinic Acid Production and Antioxidant System in Melissa officinalis L. Seedlings”, Annual Research & Review in Biology, 4(22), pp. 3359-3372. doi: 10.9734/ARRB/2014/9300.

 

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