Comparison of different methods for separation of haploid embryo induced through irradiated pollen and their economic analysis in Melon (Cucumis melo var. inodorus).

Irradiated pollen technique is the most successful haploidization technique within Cucurbitaceae. After harvesting of fruits pollinated with irradiated pollen, classical method called as "inspecting the seeds one by one" is used to find haploid embryos in the seeds. In this study, different methods were used to extract the embryos more easily, quickly, economically, and effectively. "Inspecting the seeds one by one" was used as control treatment. Other four methods tested were "sowing seeds direct nutrient media," "inspecting seeds in the light source," "floating seeds on liquid media," and "floating seeds on liquid media after surface sterilization." Y2 and Y3 melon genotypes selected from the third backcross population of Yuva were used as plant material. Results of this study show that there is no statistically significant difference among methods "inspecting the seeds one by one," "sowing seeds direct CP nutrient media," and "inspecting seeds in the light source," although the average number of embryos per fruit is slightly different. No embryo production was obtained from liquid culture because of infection. When considered together with labor costs and time required for embryo rescue, the best methods were "sowing seeds directly in the CP nutrient media" and "inspecting seeds in the light source."

Critical phases in the seed development of common juniper (Juniperus communis).

Common juniper (Juniperus communis L.) populations in northwest European lowlands are currently declining in size and number. An important cause of this decline is a lack of natural regeneration. Low seed viability seems to be one of the main bottlenecks in this process. Previous research revealed a negative relation between seed viability and both temperature and nitrogen deposition. Additionally, the seeds of common juniper have a variable ripening time, which possibly influences seed viability. However, the underlying mechanisms remain unresolved. In order to elucidate this puzzle, it is important to understand in which phases of seed production the main defects are situated, together with the influence of ripening time. In this study, we compared seed viability of populations with and without successful recruitment. We examined three seed phases: (i) gamete development; (ii) fertilisation and early-embryo development; and (iii) late-embryo development. After the first two phases, we found no difference in the percentage viable seeds between populations with or without recruitment. After late-embryo development, populations without recruitment showed a significantly lower percentage of viable seeds. These results suggest that late-embryo development is a bottleneck in seed development. However, the complex interaction between seed viability and ripening time suggest that the causes should be in the second seed phase, as the accelerated development of male and female gametophytes may disturb the male-female synchrony for successful mating.

Mechanism of seedlessness in a new lemon cultivar 'Xiangshui' [Citrus limon (L.) Burm. F].

Seedlessness is an important economic trait of lemon. Understanding the cellular and molecular mechanisms of seedlessness in 'Xiangshui' lemon requires detailed data on pollen and embryo sac fertility, embryo development and compatibility mechanisms governing self- and cross-pollination. The results of the current study indicate that the fertility of pollen and mature embryo sac remains normal. When flowers were self- or cross-pollinated, pollen grains of 'Xiangshui' were able to germinate on the stigma. In the case of self-pollination, pollen tubes became twisted, tube tips enlarged and tubes ruptured in the bottom of stigma. Following cross-pollination, tubes were able to grow normally in the style and ovary and enter the embryo sac, where double fertilization took place. Embryonic development resulting from cross-pollination was normal. After cross-pollination, the zygote began to divide at 2 weeks post-pollination, with early globular embryos observed after 3 weeks, globular and heart-shaped embryos at 4 weeks, torpedo-shaped embryos at 5 weeks, cotyledonary embryos at 6 weeks and thereafter germinable seeds. After self-pollination, however, ovules began to abort at 2 weeks post-pollination, with ovules disappearing at 5 weeks, ultimately producing seedless fruits. Emasculated unpollinated flowers also developed into seedless fruits, indicating that seedlessness contributes to parthenocarpy. However, gametophytic self-incompatibility has a major role in seedlessness in 'Xiangshui' lemon by blocking fertilization at the bottom of the stigma.

Pectin methylesterases induce an abrupt increase of acidic pectin during strawberry fruit ripening.

The decrease of strawberry (Fragariaxananassa Duch.) fruit firmness observed during ripening is partly attributed to pectolytic enzymes: polygalacturonases, pectate lyases and pectin methylesterases (PMEs). In this study, PME activity and pectin content and esterification degree were measured in cell walls from ripening fruits. Small green, large green, white, turning, red and over-ripe fruits from the Elsanta cultivar were analyzed. Using the 2F4 antibody directed against the calcium-induced egg box conformation of pectin, we show that calcium-bound acidic pectin was nearly absent from green and white fruits, but increased abruptly at the turning stage, while the total pectin content decreased only slightly as maturation proceeded. Isoelectrofocalisation performed on wall protein extracts revealed the expression of at least six different basic PME isoforms. Maximum PME activity was detected in green fruits and steadily decreased to reach a minimum in senescent fruits. The preliminary role of PMEs and subsequent pectin degradation by pectolytic enzymes is discussed.

Barriers to sexual reproduction in Polygonum viviparum: a comparative developmental analysis of P. viviparum and P. bistortoides.

Polygonum viviparum is widely distributed in arctic and alpine regions of the northern hemisphere. Fruit set has never been observed in North American populations and has been reported only very rarely in Europe. Although this species is extremely well studied, the impediments to successful fruit production are unknown. We investigated the sexual reproductive process in P. viviparum growing in the southern Colorado Rocky Mountains. For comparison, we also examined this process in the sympatric congener P. bistortoides, in which reproduction is exclusively sexual. Lack of viable fruit production in P. viviparum has no single developmental explanation; defects occur in each of the processes and structures associated with sexual reproduction studied, yet, these processes and structures also appear to function normally in at least some flowers or individuals. Development is abnormal in many ovules of P. viviparum, however, comparison with P. bistortoides shows that these abnormalities do not contribute to differences in seed production between the two species. The virtual absence of sexual reproduction in P. viviparum appears to be due largely to a low rate of fertilization and to embryo/fruit abortion.