The Effects of 60Co γ-Irradiation on Development of Crocus sativus L.
Z. Jun, C. Xiaobin, C. Fang
Life and EnvironmentScienceCollege
ShanghaiNormalUniversity
Shanghai 200234
PR China
Keywords:corm, development, saffron
Abstract
Effects of 0~25Gy 60Co γ-rays irradiation on the development of Crocus sativus L. corms(12~14g weight) were investigated in this paper The results showed that irradiation at the dose of 5～10Gy can stimulate the flowering of saffron, and can improve the harvest ration of offspring. It is concluded that 5～10Gy irradiation is suitable mutation dose for 12-14g weight corms of saffron.
INTRODUCTION
Saffron(Crocus sativus L.)stigma has high medicinal value, also called “plant gold”. Thus most research on saffron focuses on selection and exsomatie biosynthesis of its effective components. Saffron species source can be extended only through asexual multiplication, resulting in saffron quality degradation, which has been a big obstacle to saffron breeding, species quality storage and multiplication. It is a common belief that saffron infertility results from its triploid. We also discover during our research that sperm and egg cells maldevelopment and incomplete sprouting of pollen tube happen to saffron. The irradiation technique is very widely used for irradiation mutagenesis(Sun et al., 2005), species breeding and selection(Chen et al., 2004) farm product storage(Xu et al., 1998; Lao et al.,2004), plant physiology(Zhang et al., 2002), flower antistaling(Wit et al., 1985; Yang, 1995; Hayashi et al., 1996),etc. In this experiment, 60Co γ-ray is used for irradiation mutagenesis treatment to saffron corm in order to research its effect on saffron development and expect to provide reference for the further research on saffron irradiation mutagenesis, species breeding and selection, fertility and secondary metabolism ingredients, etc.
MATERIALS AND METHODS
Saffron corms are from Key Lab of Sichuang Province Resource Biology and Biological Pharmaceutical Engineering, having weight between 12 and 13.96g.Irradiation treatment is performed in Biotechnology and Nuclear Technique Research Institute of Sichuan Academy of Agricultural Science. Ray source is 60Co, irradiation doses are 0, 5, 10, 15, 20 and 25Gy respectively and dose rate is 4.018Gy/min. 35 corms are treated at one time.Saffron corm implantation starts in middle October and the blooming season starts early in November. Leaf length and style length for each corm and changes of flower organ size, length and quantity must be recorded on the flowering day to investigate the effects of irradiation treatment on foliation, flowering and flower organ mutation. Five-point sampling method is used to sample two individual plants for each point. Young plant height must be measured in November and next February respectively to investigate the effect of the irradiation treatment on sprout growth. Corms maturing stage starts in March, and cormlet harvest and test start in May.The fruit inception treated with 10Gy irradiation is fixed, embedded, cut and compared to the fruit inception at blooming season on the corm flowering day to investigate the effect of the irradiation treatment on the fruit inception development. Flowering rate (%)=(flower number/ total corm number)×100%, and survival rate (%)＝(the number of survivable young plants/total corm number)×100%.
RESULTS AND DISCUSSION
The Effect of Irradiation on Saffron Foliation and Flowering
As seen from Table 1, the irradiation treatment inhibits leaf and style growth with increasing dose, and the entire plant is shortening in comparison with the control plant, the flowering rate after 10-25Gy irradiation treatment is all 108.6 %(some corms have two flowers)and is increasing based on the control and stimulates flowering appropriately. No foliation happens to the corms treated with 20-25Gy irradiation at blooming season(Fig. 1), foliation ratio after 5Gy irradiation treatment is 28% and foliation ratio after 5 and 10Gy irradiation treatment is 00%.
The Effect of Irradiation on Fruit Inception Development
As seen from figure 1, the fruit inception of saffron treated with 10Gy irradiation has the same structure with the control. It has multi-ovule fruit inception including 2-12 ovules and an eight-cell embryo sac. It’s also known from Fig. 1 that pollen can sprout on the stigma.
Flower Organ Mutation
Normal flower organ size: 3.5cm×1.2cm petal, 2.2cm anther, 6-7cm style and 4-5cm stigma. Over 20Gy irradiation leads to flower organ mutation, showing significant shortening of petal, stigma, style and anther, for example, petal size is only 2.8cm×0.5cm, 3.2cm×1.0cm, 3cm×0.9cm; anther is 0.7 or 1cm long; style is 2.8, 3.5 or 5cm long, and stigma is 0.7, 3.1 or 3.4cm long.
Petal is the flower organ whose development is most greatly affected by the irradiation, having four-petal and three-petal mutation; The second on is stigma, have two-stigma mutation; anther is steadier, with no quantity mutation and only length change.
The Effect of Irradiation on Florescence
From November 7th to 13th, the corm treated with each dose irradiation starts flowering. The corm treated with 5Gy irradiation has the same blooming season with the control(November 7th), and others has the blooming season 3-6 days later than the control.
The stage of full bloom starts when the flowering rate reaches 80%. The stage of full bloom after each dose irradiation treatment and the stage of full bloom for the control are November 15th(10Gy), November 15th(CK), November 19th (5Gy), November 21st (15Gy), November 21st (20Gy)and November 23rd (25Gy) respectively. The blooming season after 10Gyirradiation treatment is three days later than the control, with the same stage of full bloom with the control; and the stage of full bloom after 5Gy treatment is four days later than the control and that after 10Gy treatment. Whether this result results in corm size variation or not will be verified. The results for 15, 20 and 25Gy irradiation treatment show that the saffron has late stage of full bloom mainly due to the increased irradiation dose (Table 2).
The Effect of Irradiation on Young Plant Growth
As seen from Table 3, the corms treated with 20 and 25Gy irradiation are more greatly affected by irradiation, young plant hardly grows and can’t produce cormlet in November; the corms treated with 5 and 10Gy irradiation have lower survival rate than the control up to 34% and 31% respectively; the corms after 5, 10 and 15Gy irradiation all produce small corm and harvest cormlet next April.
The cormlet test results in Table 4 show that the harvested corms weigh 14 and 9.3g and have flowering ability after 5and 10Gy irradiation treatment, and the harvested corm weighs 7.7g and has only vegetative growth after 15Gy irradiation treatment. There are great change and variation between various irradiation treatments in Crocin, Safranal and Picrocrocin in saffron stigma, which happen in the second year of implantation(See Table 5 or Fig. 2).
The irradiation has various effects on saffron development.13-14g corm has flowering rate up to 108.6% after 10-25Gy irradiation treatment, with 2 percentage points higher than the control, which shows that the irradiation treatment leads to flowering stimulation to the corm with a certain weight and the effect on accumulation of secondary metabolism. The harvested cormlet has flowering ability only after 5 and 10Gyirradiation treatment, and therefore it is primarily determined that the optimal irradiation mutagenesis dose is 5-10Gy for the corn over 12g.
ACKNOWLEDGEMENTS
Thanks to Funding Supported by Shanghai Municipal Education Commission (No: 04DB10).
Literature Cited
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Table 1. Effects of below 25Gy dose on foliation and blooming
Item / Dose(Gy)0 / 5 / 10 / 15 / 20 / 25
Length of sprout (cm) / >6 / 3-6 / 2-5 / 0-4 / 0 / 0
Flowering ratio (%) / 106.7 / 88.6 / 108.6 / 108.6 / 108.6 / 108.6
Length of style (cm) / 10.5 / 8-10 / 7.5-8.5 / 6-7 / 6-7 / 7.7
Foliation ratio (%) / 100 / 100 / 100 / 28 / 0 / 0
Table 2. Effect of irradiation on florescence
Dose(Gy) / Date (November)7 / 10 / 11 / 12 / 13 / 14-15 / 16 / 17-19 / 20-21 / 22-23
CK / 1 / 9 / 4 / 4 / 5 / 5* / 1 / 1 / 1 / /
5 / 1 / 2 / 5 / 1 / 10 / 6 / 1 / 2* / 1 / 2
10 / / / 3 / 3 / 1 / 7 / 15* / 8 / / / 1 / 3
15 / / / / / 1 / 1 / 7 / 5 / 2 / 8 / 8* / 5
20 / / / / / / / 2 / 2 / 10 / 4 / 5 / 8* / 4
25 / / / / / / / / / 4 / 5 / / / 6 / 7 / 9*
*Note: The data in this table is the flower number on the day of investigation, wherein means that the stage of full bloom has come.
Table 3. Effect of irradiation on seedling
Item / Dose (Gy)0 / 5 / 10 / 15 / 20 / 25
Young plant height a(cm) / 22 / 21 / 15 / 10 / 8 / 7
Young plant height b(cm) / 42 / 38.6 / 25.6 / 14.3 / 8.6 / 8.3
Survival rate (%) / 90(27/30) / 34(12/35) / 31(11/35) / 8.6(3/35) / 0(0/35) / 0(0/35)
Note: The data in this table a is the young plant height on November 29th, b is young plant height on February 21st, and the data in the bracket is the number of survivable young plants/total corm number.
Table 4. The cormlets harvested after different irradiation treatment
Test item / Dose (Gy)0 / 5 / 10 / 15 / 20 / 25
No.of harvested corms / 13 / 11 / 10 / 3 / 0 / 0
Weight of harvested corms(g) / 196 / 154 / 126 / 23.2 / 0 / 0
No. of planting corms / 30 / 35 / 35 / 35 / 35 / 35
Weight of per corm (g) / 15 / 14 / 9.3 / 7.7 / 0 / 0
Harvest ratio(%) / 43.3 / 31.4 / 28.5 / 8.5 / 0 / 0
Table 5. The abs of secondary metabolism of irradiated saffron
Secondary metabolits / 5Gy / 10Gy / 15Gy
T.f.year / T.s.year / T.f.year / T.s.year / T.f.year / T.s.year
Crocin / 29.65 / 16 / 25.6 / 3 / 168.12 / 4.5
Safranal / 43.12 / 2.75 / 25.24 / 1.95 / 41.04 / 3.5
Picrocrocin / 61.72 / 8.25 / 45.3 / 3.4 / 72.56 / 6.25
Abbreviations: T.f.year: The first year; T.s.year: The secondary year
Fig. 1. Irradiated corm in bud; 2 Irradiated corm in flowering; 3 Ovary slice of Irradiated corm; 4 Germination of pollens of irradiated corm on stigma ac: antipodal cell; pn: polar nuclei; sy: synergid; ec: egg cell pt: pollen tube; pl: plloen; sp: stigma papilla cell
Fig. 2. chematic igure for ultraviolet radiation analysis of effective components in the stigma treated with 5Gy irradiation