柚子(Citrus grandis Osbeck)S-like核酸酶基因CgSL1的分离与特征分析

从柚子(CitrusgrandisOsbeck)2个自交不亲和品种溪蜜柚和度尾蜜柚的花柱中克隆出一个类似S核酸酶基因CgSL1(C.grandisS-likeRNase),它的cDNA序列全长1074bp,编码297个氨基酸。通过与其它植物S-like核酸酶和S核酸酶氨基酸序列进行比较,发现CgSL1类似于S-like核酸酶,与拟南芥中的RNS2一致性为62.5%。对CgSL1的表达分析表明该基因在花柱、花药、叶片不同器官以及花柱的不同发育阶段均有表达,且在花柱中的表达随衰老增强,由此推测它可能与衰老有关。     

Leaching Soluble Salts Increases Population Densities of Tylenchulus semipenetrans

The effect of salinity on population densities of Tylenchulus semipenetrans was measured on 3-month-old salt-tolerant Rangpur lime growing on either loamy sand, sand, or organic mix and on 4-month-old salt-sensitive Sweet lime in organic mix. Salinity treatments were initiated by watering daily with 25 mol/m³ NaCl + 3.3 mol/m³ CaCl₂ for 3 days and every other day with 50 mol/m³ NaC1 + 6.6 mol/m³ CaC1₂ for one week, with no salt (NS) treatments as controls. Salinity was discontinued in one treatment (DS) by leaching with tap water prior to inoculation with nematodes, whereas the continuous salinity (CS) treatment remained unchanged. Overall, in Rangpur lime organic soil supported the highest population densities of T. semipenetrans, followed by loamy sand and sand. The DS treatment resulted in the highest (P ≤ 0.05) mean population densities of T. semipenetrans in the three soil types. Similarly, the DS treatment in Sweet lime resulted in the highest (P ≤ 0.05) nematode populations. The DS treatment predisposed citrus to nematode infection through accumulated salt stress, whereas leaching soluble salt in soil solution offered nematodes a suitable nonosmotic habitat. Nematode females under the DS treatment also had the highest (P ≤ 0.05) fecundity.     

Isoenzyme pattern of superoxide dismutase in different varieties of citrus plants

Superoxide dismutases (SOD; EC 1.15.1.1) in leaves from different cultivars of citrus plants were characterized using isoelectric focusing in polyacrylamide gels. The plants studied included Citrus limonum R. (cvs Verna, Fino, and Eureka), C. paradisi Mac (cvs Red Blush and Marsh), C. aurantium L. (cv. Comun), C. sinensis L. Osbeck (cvs Navel, Valencia, and Salustiano), and C. reticulata B. (cv. Satsuma). The three molecular forms of SOD were distinguished from each other by their different sensitivity to cyanide and H₂O₂. In C. limonum leaves, four Cu,Zn-SODs, three Fe-SODs and two Mn-SODs were present. However, in leaves from different varieties of C. sinensis, C. paradisi, C. aurantium and C. reticulata the activity and number of Fe-SOD isoenzymes were lower than in lemon leaves, whereas the number of MN-SOD isozymes was increased. Cu,Zn-SODs did not show significant variations in the different species and cultivars. The identification of Fe-SODs in several species of the plant family Rutaceae extends the small number of higher plants where the presence of these Fe-containing metalloenzymes has been demonstrated. Results obtained may be useful from an evolutionary viewpoint and also in mineral nutrition studies using SOD isozymes as markers of functional metals.     

Citrus meletensis (Rutaceae), a new species from the Pliocene of Valdarno (Italy)

There are few fossil remains that are assigned or compared toCitrus. A new and characteristic leaf from the Pliocene of Italy is described asCitrus meletensis and its systematic position within theRutaceae is discussed. Together with other sparse remains that are reviewed here it confirms the existence ofCitrus in the European Tertiary.