Irradiated Shoots Research Articles

Comprehensive effects of heavy-ion beam irradiation on sweet potato (Ipomoea batatas [L.] Lam.).

Sweet potato is a major root crop with nutritious tuberous roots. The mechanism of tuberous root development has not yet been adequately elucidated. Genetic resources are required to develop the molecular understanding of sweet potato. Heavy-ion beams were applied to hexaploid sweet potato for an increase in genetic variation, after which the comprehensive effects of heavy-ion beam irradiation were investigated. In vitro cultured shoots with an axillary bud of 'Beniharuka' were irradiated with Ar-ions at a dose of 1-5 Gy and C-ions at a dose of 5-20 Gy, and three irradiated lines were separated from each irradiated shoot. The shoot regeneration was inhibited at high doses of each ion irradiation. Ar-ion irradiation had an especially high biological effect on shoot regeneration. A total of 335 lines were obtained, consisting of 104 and 231 lines derived from Ar- and C-ion irradiation, respectively. The change in the DNA content of the lines was analyzed by flow cytometry to evaluate the irradiation-induced damage to the DNA. The two lines demonstrated significant differences in the DNA content and changes at the chromosome level. The screening for the morphological mutants was conducted in the field. Some irradiated lines showed inhibited or no tuberous root phenotype as mutant candidates. Additionally, the high-yield mutant candidates were dominated by Ar-ion irradiation. It was indicated that heavy-ion beam mutagenesis is effective in broadening the range of the phenotypes corresponding to tuberous root formation in hexaploid sweet potato.

Gamma irradiations induced morphological and biochemical variations in in vitro regenerated ginger (Zingiber officinale rosc.)- an invaluable medicinal spice

Purpose To evaluate the effect of gamma irradiations on morphological and biochemical variations of in vitro shoots, regenerated plants and rhizomes of ginger (Zingiber officinale Rosc.) var. Himgiri. Materials and methods In vitro established shoot cultures were treated with different doses of gamma irradiations (10–100 Gy). Nonirradiated shoots were used as controls. Radio sensitivity of shoots and in vitro growth parameters were recorded. Surviving shoots along with controls were multiplied, rooted and hardened. Irradiation effect on chromosomes was evaluated by comparing with controls. Various morphological and biochemical observations were recorded in regenerated plants and rhizomes and compared to controls. Results Irradiated shoots showed decline in survival percentage (95% in 10 Gy to 12.33% in 100 Gy) with increase in dose rate after 4 weeks of irradiation. Shoot survival significantly decreased with irradiation dose rate above 20 Gy. Shoot multiplication rate showed an increase from 1:2 in 1st subculture to 1:9 after 5th subculture, in 10 Gy irradiated cultures with 4.5 cm average length of shoots and 8.19 number of leaves after 5th subculture. Average rooting showed an increase from 15.55% after 2nd subculture to 100% after 5th subculture, in 10 Gy irradiated shoots; however, no multiplication and rooting was observed in higher doses. In vitro rooted shoots were subjected to hardening with 100 percent survival in a mixture comprised of soil, cocopeat and FYM. One-year-old hardened plants when observed for morphological variations showed nonsignificant variations in comparison to controls. Rhizomes obtained from 10 Gy irradiated plants showed enhanced concentration of 6-gingerol and reduced crude fiber content when compared with controls. Conclusions Gamma irradiation doses up to 10 Gy resulted in nonsignificant phenotypic variations but can positively affect biochemical composition of rhizomes leading to development of biochemically improved mutant lines of ginger with increased 6-gingerol and lowered crude fiber content. Therefore, suggesting the lower doses of gamma irradiations for improvement of biochemical constituents in vegetatively propagated plants.

In vitro selection of gamma irradiated shoots of ginger (Zingiber officinale Rosc.) against Fusarium oxysporum f.sp. zingiberi and molecular analysis of the resistant plants

In the present investigation, an attempt was made to develop Fusarium yellows resistant plants of ginger (Zingiber officinale Rosc.) var. Himgiri using in vitro mutagenesis and selection technique. Axenic in vitro cultures were subjected to gamma irradiation (10–100 Gy) for mutation induction. LD50 was calculated after every 4 weeks, and was observed to be 15 Gy after 16 weeks of irradiation. Surviving 10 Gy irradiated shoots were cultured on selective medium containing different concentrations (0–20%) of fungal culture filtrate (FCF) obtained from Fusarium oxysporum f.sp. zingiberi for in vitro selection. FCF concentration of 17.5% in the selective medium was found to be the highest on which 5% shoots survived after first selection cycle, which further reduced to 1.1% after third continuous cycle of selection. It was followed by 4.3% shoot survival after third selection cycle on 15% FCF concentration. Surviving, selected shoots from 15 and 17.5% FCF were multiplied on multiplication medium and rooted plantlets were hardened with 100% survival. On in vivo evaluation 46.4 and 52% plants selected at 15 and 17.5% FCF were found to be highly resistant. Molecular analysis with disease specific SSR primers differentiated between FCF selected, tissue culture propagated and gamma irradiated plants. Two unique bands were obtained in 15 and 17.5% FCF selected plantlets with GIN 6 and GIN 9 primers, sequencing, of which showed 98 and 97% homology with disease resistance protein-like gene CC-NBS-LRR from clones ZwP627 and ZoP620 of Z. officinale. After in vivo bioassay, SSR analysis of selected highly resistant plants again confirmed the unique bands with both the primers. The DNA sequences obtained from these primers have been published in GenBank under accession number MN497252 and MN497253. A combination of in vitro mutagenesis using gamma irradiations followed by selection mediated by fungal culture filtrate produced ginger plants resistant to Fusarium yellows disease.

Morphological Variation and Beta Carotene Contents of Several Clones of Ubi Kuning Cassava Genotype Derived from Irradiated Shoot in vitro

In line with the increase in cassava production and the development of nutrient-rich cassava in order to support national food diversification and biofortification programs, the selection of selected varieties of cassava varieties, which are superior in nutrients especially rich in beta carotene is very necessary. Beta carotene is an important source of antioxidants to scavange free radicals and is a provitamin A precusor to form vitamin A. The development of superior cassava riching in beta carotene can be done through the mutation approach with gamma irradiation. The observation of changes in morphological characters and levels of beta carotene from irradiated cassava need to be done to get the superior beta carotene cassava clone candidates, which could be developed in the future. This experiment was conducted at the Biotechnology Research Center, LIPI. The sample used in this study originated from in vitro shoots from several Ubi Kuning clones resulting from 10 Gy radiation, which were then transferred to the field. Observations of morphological characters and levels of beta carotene of Ubi Kuning were carried out in the third generation, which was harvested at the age of 10 months. The morphological analysis of irradiated Ubi Kuning showed that there was a difference in the intensity of tuber color between some of irradiated Ubi Kuning clones compared to the control. The determination of beta carotene levels based on the standard beta carotene curve found that the highest content of beta carotene was found in the UK Rad 3.4 clone with beta carotene content of 0.252 μg / mL compared to the control (0.219 μg / mL). The lowest beta carotene content was obtained in UK Rad 3.3 (0.048 μg / mL), followed by UK Rad 3.2 (0.221 μg / mL) and UK Rad 4.1 (0.120 μg / mL). This shows that the irradiated Ubi Kuning at dosage of 10 Gy caused variations in the intensity of tuber colors and the content of beta carotene from the cassava.Keywords: Ubi Kuning, beta carotene, Gamma light irradiation

The Effect of Gamma Irradiation on the Growth and Multiplication of the In Vitro Shoot of Patchouli (Pogostemon cablin Benth.)

The objective of this research was to evaluate the effect of gamma irradiation on shoot growth and multiplication of Patchouli (Pogostemon cablin Benth.) Two weeks-old in vitro shoots were irradiated gamma-ray, at doses of 0, 15, 30, 45, 60, and 75 Gy. The control shoot was not irradiated. The irradiated shoots were cultured on Murashige and Skoog (MS) medium supplemented with 0.1 mg.L-1 NAA and 0.3 mg.L-1 BA and incubated in a growth room for eight weeks at a temperature of 25±2°C. The results showed that the gamma irradiation inhibited the growth and multiplication of shoots. Explants irradiated with high-dose gamma-ray (45-75 Gy) had not formed shoot in four weeks of culture, while 58.3-83.3% of the explants without irradiation or irradiated at low doses 15 and 30 Gy formed shoots. The higher irradiation doses increased percentage of browning explants and reduced the percentage of forming shoots. Within the eight weeks of culture, explant without irradiation was able to form shoots at the percentage of 100% with 24 shoots per explant, while explants irradiated at 15-45 Gy were able to grow form shoots at the percentage of 77.7-95.5%. The high doses-irradiated explants (60 and 75 Gy) were only able to form shoots less than 13-20%, with 2-3 shoots per explant.Keywords: Gamma rays (Gy), in vitro shoot, Pogostemon cablin Benth.

Response of irradiated chilli pepper shoots (Capsicum annuum. L.) propagated in vitro to drought stress tolerance

Drought stress in plants caused by water deficiency. In Vitro selection with mutation techniques offered stress tolerance in plants. Shoot tips of chilli pepper (Capsicum annuum . L.) exposed for gamma radiations at the doses (0, 10 and 20 Gy). Irradiated shoots were exposed to stress tolerance in the presence of Polyethylene Glycol (PEG 6000) in MS medium. Analysis of variance results for all characters studied were found to be significant, highest dose 20 Gy interaction with 40 g.l-1 of PEG gave highest number 6.2 shoot. explant-1 whereas 10 Gy and 40 g.l-1 of PEG gave highest plant height 6.04 cm. Further, higher accumulation of proline reached 26.97 mg. g-1 at interaction of 20 Gy+ 60 g.l-1 PEG while highest accumulation of CHO found at 20 Gy+ 40 g.l-1 PEG.

Gamma irradiation induced effects on in vitro shoot cultures and influence of monochromatic light regimes on irradiated shoot cultures of Dendrobium sonia orchid

The effects of gamma radiation and monochromatic lights on growth of in vitro shoot cultures of orchid, Dendrobium sonia, were investigated. The gamma irradiated shoot cultures grown under white, blue, yellow and red monochromatic lights exhibited differential growth pattern. Shoot cultures gamma irradiated at 15–45 Gy showed reduced shoot length, fresh weight and leaf area. The monochromatic light significantly influenced survival rate and growth of irradiated shoots. The yellow and red light treatments positively influenced survival of gamma irradiated shoots with significant increase in fresh weight, shoot length and chlorophyll content. Yellow light was found to be most effective as leaf area was increased across the radiation dose range (15–100 Gy) compared to red light. The results demonstrated that the method of post-irradiation exposure could be useful to improve growth of gamma irradiated in vitro shoots, and help to recover orchid mutants with novel modifications.

MUTATION INDUCTION OF ANTHURIUM ANDREANUM USING GAMMA RADIATION

Anthuriums are one of the most popular ornamental plants in Thailand. Hence, more attractive cultivars of plants are needed to promote its cultivation industry. This study aimed to produce a new cultivar of Anthurium andreanum through mutation techniques using gamma radiation. Multiple shoots of three-month-old ‘Angle’ were acute irradiated with gamma ray at a dose of 0, 10, 20, 30, 40 and 50 gray. Percentage of survival shoots tended to decrease with the increasing doses. Shoots irradiated at 40 and 50 gray could not survive after culturing in M1V2 (4 months). Gamma radiation at 19.99 gray gave 50% of survival rate (LD50). Non-irradiated shoots in M1V1 to M1V4 showed the highest percentage of shoot induction, number of shoot per explant, plant height, number of leaves, leaf length and leaf width, significant difference from irradiated shoot. Within irradiated treatments, shoots treated with 10 gray showed all of the mentioned characteristics of higher quality or quantity than the others. In contrast, they had the lowest number of chloroplast, stomata concentration, length and width of stomata and guard cell. At M1V4 (8 months), plants induced from non-irradiated shoots produced normal leaves, but plants induced from shoots of 10 gray produced the highest percentage of mosaic leaf, significantly different from the other doses. Genetic variations of mutation plants were investigated by AFLP technique. A total of twenty primers were used. Results showed that only ER-ACA/MS-CAG primer presented polymorphism of DNA banding in mosaic leaves comparing to normal leaves of the irradiated plants. There was no different characteristic found in normal leaves of both irradiated and non-irradiated plants. The mutation plants with mosaic leaves are potentially cultivated as a new Anthurium cultivar.

APPLICATIONS OF CITRUS SHOOT-TIP GRAFTING IN VITRO

The main application of shoot-tip grafting in vitro (STG) is to control graft-transmissible pathogens that requires the use of healthy trees in the new plantings. The routine application of STG using 0.1-0.2 mm shoot tips is very efficient for elimination of all citrus graft-transmissible pathogens from local or imported varieties. It has allowed the recovery of hundreds of healthy cultivars and the planting of hundreds of millions of healthy certified trees worldwide. Only in Spain about 140 million certified nursery plants propagated from micrografted plants have been planted. STG is also a very useful technique for regeneration of elite genotypes in several research areas. In vitro grafting for these purposes may be done using larger shoots (up to 1 cm). STG is being routinely used for the following purposes: (i) Regeneration of somatic hybrids from embryos difficult to germinate; (ii) Regeneration of plants from irradiated shoots to produce seedless varieties; (iii) Regeneration of plants from haploid embryos that are very difficult to germinate. STG was used to regenerate the ‘Clemenules’ haploid plant that has been used by the International Citrus Genome Consortium to sequence the whole citrus genome; (iv) Production of stable tetraploid plants of non-apomictic genotypes, which are very useful for triploid breeding; (v) Regeneration of transgenic plants from shoots that are very difficult to root in vitro. STG has become a routine application in citrus genetic transformation.

Molecular characterization of DNA repair protein Ku70 from Vitis vinifera and its purification from transgenic tobacco

The DNA double strand break repair in plants is preferentially by non homologous end joining (NHEJ) pathway. A key protein of NHEJ pathway is Ku70. We have identified Ku70 homolog (VvKu70) from grapevine genome database. In this report we characterize a Ku70 homologue from Vitis vinifera cv. Mango. The VvKu70 expression was found to increase strongly in response to gamma radiation. The transcript level of VvKu70 was found to increase up to 36h in gamma irradiated shoots of grapevine. The expression of VvKu70 was found in many organs like stem, leaves and roots. A GFP fused VvKu70 protein was found to be nuclear localized which indicates that the VvKu70 is a nuclear localized protein. The VvKu70 identified by in silico approaches is present as a single copy number in V. vinifera cv. Mango genome. The VvKu70-GFP fused protein possesses ATPase activity and fails to bind dsDNA but binds ssDNA.

Reduced-stature Rosa species through in vitro mutagenesis

Baig, M. M. Q., Hafiz, I. A., Abbasi, N. A., Yaseen, M., Akram, Z. and Donnelly, D. J. 2012. Reduced-stature Rosa species through in vitro mutagenesis. Can. J. Plant Sci. 92: 1049–1055. Plant height is one of the main attributes affecting general appeal and beauty of roses (Rosa spp.). Among the highly scented rose species, R. gruss an teplitz, R. centifolia, and R. borboniana, have great potential horticultural and commercial value. However, their large plant size detracts from recent trends towards selection of smaller plants for emerging markets and high-density plantations. This study aimed to produce reduced-stature plants through in vitro mutagenesis using gamma irradiation (Co60). Shoot tips cut from micropropagated shoots were exposed up to 120 Gy. Irradiated shoot tips were micropropagated for one culture cycle. Surviving shoots were rooted in vitro then acclimatized for 2 mo in a greenhouse. The shoot tip LD50 after gamma irradiation was species-dependent and 33–54 Gy. In this dose range, survival during in vitro rooting and acclimatization was also affected; this was 64 to 24% and 34 to 14% of control values, respectively. Acclimatized transplants were 17 to 56% smaller with 16 to 51% less leaf area compared with the controls. In order to ascertain stability putative reduced-stature roses will be monitored for vegetative and floral characteristics over the next few years. This study adds to the ongoing efforts to obtain reduced-stature rose plants for horticultural purposes.

Analysis of drought-tolerant sugar beet (Beta vulgaris L.) mutants induced with gamma radiation using SDS-PAGE and ISSR markers

Drought is one of the major environmental stresses which greatly affect the plant growth and productivity. In the present study, various doses (0–75Gy) of gamma rays were applied to investigate the effect of radiation on shoot tip explants. It was observed that the regeneration rates and plant fresh weights decreased significantly with an increase in radiation dose. The optimal irradiation doses for mutation induction were determined at 15 and 20Gy. Afterwards, the induction of somatic mutation in sugar beet (Beta vulgaris L.) was investigated by irradiation of shoot tips with 15 and 20Gy gamma rays. Irradiated shoot tips were sub-cultured and M1V1–M1V3 generations were obtained. Mutants tolerant to drought stress were selected on MS medium, supplemented with 10 and 20gl−1 PEG6000. Of the M1V3 plantlets, drought-tolerant mutants were selected. Leaf soluble proteins obtained from the control and drought-tolerant mutants were analyzed by SDS-PAGE. A total of 22 protein bands were determined and 2 of them were observed to be drought-tolerant mutants except the control. Polymorphism was also detected among the control and drought-tolerant mutants by DNA fingerprinting using ISSR markers. A total of 106 PCR fragments were amplified with 19 ISSR primers and 91 of them were polymorphic. The dendrograms were separated into two main clusters. First cluster included M8 mutant plant, which was applied 20Gy gamma radiation and regenerated on selective culture media containing 10gl−1 PEG6000 concentration, and the second cluster was further divided into five sub-clusters.

Induced mutation in rice (cv. RD 6) by tissue culture

The sterilized seeds of sticky rice cultivar RD 6 were cultured on the MS medium supplemented with 15% coconut water, 1g/l yeast extract and 0, 2, 4, 6, 8 and 10 mg/l BAP. The suitable medium for multiple shoots induction was MS medium supplemented with 15% coconut water, 1g/l yeast extract and 2 mg/l BAP giving the average of 5.47 shoots per seed. The shoots were gamma irradiated at 0 and 30 Grays. Non-irradiated and irradiated shoots were cultured on MS medium supplemented with 2 mg/l BAP and 0, 0.5, 1.0 and 1.5% NaCl. The number of non-irradiated surviving shoots on these media were 18, 15, 1 and 0 shoots, respectively, while those of irradiated shoots on the same media were 33, 29, 6 and 2 shoots, respectively. These survival plants of both groups were then transferred to grow in the pot containing sand, Yoshida’s solution and 1% NaCl. After 4 weeks of growth, 14 out of 70 irradiated plants survived but only 3 out of 34 non-irradiated ones could tolerate the high salt condition.

PENGARUH RADIASI SINAR GAMMA TERHADAP KULTUR IN VITRO TANAMAN JAHE

In vitro shoot explants of white ginger and red ginger are irradiated by two different techniques. The first, the tuber explants are irradiated by 2 levels of gamma rays namely 10 and 30 Gy. The second, the shoot explants are irradiated by 2 levels of gamma rays namely 7,5 and 12,5 Gy. The irradiated explants are regenerated on modified MS medium with BAP 2 ppm and NAA 0,25 ppm. The result show that the irradiated tuber explants with 10 and 30 Gy could not initiate new regenerant of ginger. On the other hand the irradiated shoot explants with 7,5 and 12,5 Gy have been able to influence the growth and development of shoot, leaf and root. It is indicated that the level of gamma rays irradiation on shoot explants influences the induced putative mutant of ginger. However, the sprouting of red ginger on 12,5 Gy is higher and faster than 7,5 Gy, and white ginger as well as control. The other morphological characters have not been able to be identified, the experiment are still in process to detect the mutagenic influences.

The Effects of Gamma Irradiation on the Growth and Propagation of <em>In-Vitro</em> Chrysanthemum Shoot Explants (cv. <em>Yellow Puma</em>)

The study on the effect of gamma irradiation on in-vitro shoot growth of chrysanthemum cv. Yellow Puma has been carried out. The aim of the study was to observe genetic variability of shoot growth caused by gamma irradiation. Shoot explants with four leaves were irradiated by gamma with dose of 10, 15 and 20 Gy with 3 replications at each of dose. The irradiated shoot explants were then transferred into fresh MS solid medium and placed in a growth room. Observation was performed on number of leaves and branches on M1V0 generation, while plantlets height and number of branches were observed a M1V1 generation. Number of survival plantlets and multiplication rate on three subsequent subcultures were observed as well. Results showed that gamma rays with dose of 20 Gy inhibited growth of leaves as much as 50% compared to control (shoots without irradiation), and branches 73.7% in three weeks. Observation on multiplication rate at M1V1 generation showed that gamma irradiation with dose of 10 Gy promoted multiplication rate as much as 10% higher than control. It can be concluded that in vitro mutagenesis using gamma iradiation with dose of 10 to 15 Gy can be used for inducing genetic variability of chrysanthemum cv. Yellow Puma. Received: 18 December 2008; Revised: 10 August 2010; Accepted: 30 August 2010

Towards in vitro selection studies for salinity tolerance in Canino apricot cultivar. Effect of gamma irradiation on in vitro mutation and selection for salt-tolerance

In vitro mutation method was used to obtain salt-tolerant clone in apricot. Small propagules of Canino apricot cultivar were irradiated with gamma ray at doses of 0, 10, 25, 35, 50, 75 and 100 Gy. After 30 days from treatment, both the radio sensitivity and post-irradiation recovery were assessed as the number of proliferated shoots per explants, fresh weight of cultures, shoot length and productivity of irradiated explants. A sudden and sharp decrease in the survival percentage occurred with the dose 75 Gy, while the highest dose (100 Gy) was lethal for all propagules. A marked decline in the number of regenerated shoots per explant and fresh weight of produced cultures was associated with an increase of irradiation doses. Doses in the range of 10-75 Gy, which preserved high survival percentage of irradiated explants, seemed to be more suitable for in vitro mutation in Canino apricot cultivar. Irradiated shoots were exposed to different concentrations of NaCl which were added to the multiplication medium at the rates of 25, 50, 75, 100, 125 mM and after 30 days, vigorous shoots were selected from salinity treatments. In conclusion, apricot tissues exposed to different doses of gamma irradiation in the range of 10-75 Gy, followed by culturing the plantlets produced in a medium containing additional salts (ranging from 25 to 125 mM) can be considered a good method to identify the most tolerant mutants to salts in apricot cultivars.

Targeted Irradiation of Shoot Apical Meristem of Arabidopsis Embryos Induces Long-Distance Bystander/Abscopal Effects

Bystander effects induced by low-dose ionizing radiation have been shown to occur widely in many cell types and may have a significant impact on radiation risk assessment. Although the region of radiation damage is known to be much greater than the initial target volume irradiated, it remains to be seen whether this response is limited to the specific organ irradiated, spans a limited region of the body, or even covers the whole body of the target. To determine whether long-distance bystander/abscopal effects exist in whole organisms and to clarify the problem of intercellular communication, in the present study a specific cell group, the shoot apical meristem in Arabidopsis embryo, was irradiated with a defined number of protons and examined for root development postirradiation. The results showed that after direct damage to the shoot apical meristem from ion traversals, root hair differentiation, primary root elongation and lateral root initiation were all inhibited significantly in postembryonic development, suggesting that radiation-induced long-distance bystander/abscopal responses might exist in the whole organism. To further scrutinize the mechanism(s) underlying these inhibitory effects, a DR5-GUS transgenic Arabidopsis was used. The results showed that accumulation of the reporter GUS gene transcript in irradiated shoot apical meristem embryos decreased in the postembryonic development. Treatment with either 2,4-dichlorophenoxyacetic acid, a synthetic plant auxin, or DMSO, a effective reactive oxygen species (ROS) scavenger, could rescue the reporter GUS enzyme accumulation and the length of primary root in irradiated shoot apical meristem embryos, indicating that ROS or probably the ROS related auxin and auxin-dependent transcription process may be involved in radiation-induced long-distance bystander/abscopal effects.

Red light causes a reduction in IAA levels at the apical tip by inhibiting de novo biosynthesis from tryptophan in maize coleoptiles

When maize coleoptiles were unilaterally exposed to red light (7.9 micromol m(-2)s(-1) for 5 min), 3 h after treatment IAA levels in coleoptiles decreased in all regions, from top to basal, with levels about 60% of dark controls. Localized irradiation in the 5 mm top zone was sufficient to cause the same extent of IAA reduction in the tips to that in the tips of whole irradiated shoots. When coleoptiles were treated with N-1-naphthylphthalamic acid (NPA), an accumulation of IAA in the tip and a decrease of diffusible IAA from tips were simultaneously detected. IAA accumulation in red-light treated coleoptiles by NPA was much lower than that of dark controls. NPA treatment did not affect the content of conjugated IAA in either dark or light treated coleoptile tips. When (13)C(11) (15)N(2)-tryptophan (Trp) was applied to the top of coleoptiles, substantial amounts of stable isotope were incorporated into free IAA in dark and red-light treated coleoptile tips. The ratio of incorporation was slightly lower in red-light treated coleoptile tips than that in dark controls. The label could not be detected in conjugated IAA. The rate of basipetal transport of IAA was about 10 mm h(-1) and the velocity was not affected by red light. These results strongly suggest that red light does not affect the rates of conversion of free IAA to the conjugate form or of the basipetal transport, but just reduces the IAA level in the tips, probably inhibited by IAA biosynthesis from Trp in this region.

Effect of Gamma Rays on the Growth Performance of Bangladesh Clone Tea

The experiment was carried out to investigate the effects of gamma radiation on the early growth performance and physiological traits of BT2 clone tea, the most promising cultivar released by Bangladesh Tea Research Institute. The fresh shoot cuttings were irradiated with seven different levels of gamma radiation such as 0, 10, 20, 30, 40, 50 and 60 Gy from Cobalt 60Co source (Dept. of PlantBreeding, Bangladesh Institute of Nuclear Agriculture). Thereafter, the irradiated shoot cuttings were planted in polythene bags and kept under natural conditions. It was observed that callusing was initiated from 8th weeks after placement of tea shoot cuttings in the polythene bags and completed by 12th weeks. The morphological growth of tea shoot cuttings were recorded under varying levels of gamma radiation and growth stages. It was observed that the number of leaves, number of primary branches, base diameter, root length and total leaf area per plant significantly increased with the progress of time and increasing levels of gamma radiation, however, the plant height showed decreasing trend with the increasing levels of gamma radiation, which could be due to the change in chromosomal structure and genetic makeup. After 56 weeks of planting, the plant height, the number of leaves and primary branches per plant, base diameter, root length and total leaf area per plant recorded were 65.70 cm, 30.67, 7.33, 1.48 cm, 23.50 cm, and 1250.67 cm2 per plant respectively under the radiation level 60 Gy, whereas the corresponding figures of the above parameters at the control treatment were 76.21 cm, 18.33, 3.67, 0.92 cm, 17.75 cm and 778.33 cm2 per plant, respectively. A significant relationship was observed among the physiological growth parameters with the increasing levels of gamma radiation. The total dry matter gain, leaf area index, absolute growth rate and relative growth rate were significantly influenced with the rising levels of gamma radiation (up to 60 Gy), whereas the net assimilation rate of individual tea plant non-significantly responded as compared to those of control treatment. Finally after 56 weeks of planting, the maximum total dry weight gain, leaf area index, absolute growth rate, relative growth rate and net assimilation rate recorded under 60 Gay radiation level were 40.25 g/plant/week, 4.25, 1.18 g/week, 0.0621g/g/week and 17.07 g/m2/week respectively.

THE IMPORTANCE OF INDUCED MUTATIONS IN PEAR IMPROVEMENT

Pear production is firmly established on a limited number of well-known cultivars that appear to fulfill the requirements of the market. The pear consumer accepts more easily improvements in a standard cultivar than those that are completely new. Spontaneous and induced mutations can be of importance for pear breeding in the improvement of single traits of an already outstanding cultivar. But on the other hand, since the most appreciated pear cultivars have high degrees of heterozygosity, cross-breeding leads to high degrees of variability in the progenies, thus making troublesome the selection of new genotypes using this traditional method. Many important traits have been introduced through mutagenesis such as plant size reduction, early ripening, fruit color change, changes in blooming time, and changes in fruit quality, despite the low number of cultivars that became established commercial varieties. Variations in vegetative and fruit traits were observed in experimental orchards planted with about 5,000 self-rooted trees derived from in vitro gamma-ray irradiated shoots. Some of the observed changes improved the original cultivars allowing for an easier size control (variants for reduced size). Variants for increased sugar content and for extended shelf-life have also been found, showing that mutagenesis can change various economically important traits, thus contributing to pear breeding. The use of in vitro methodologies, the exploiting of somaclonal variation, and the setting up of early selection methods could make induced mutation techniques more reliable. The current interest in the development of induced and spontaneous interesting pear mutants is attested by a number of recent reports originated from most pear-growing countries in the world. Induced-mutation breeding has intrinsic limitations, but also offers good prospects for further contributions to pear cultivar development and improvement.