Antisense Repression of Vacuolar and Cell Wall Invertase in Transgenic Carrot Alters Early Plant Development and Sucrose Partitioning

Abstract

To unravel the functions of cell wall and vacuolar invertases in carrot, we used an antisense technique to generate transgenic carrot plants with reduced enzyme activity. Phenotypic alterations appeared at very early stages of development; indeed, the morphology of cotyledon-stage embryos was markedly changed. At the stage at which control plantlets had two to three leaves and one primary root, shoots of transgenic plantlets did not separate into individual leaves but consisted of stunted, interconnected green structures. When transgenic plantlets were grown on media containing a mixture of sucrose, glucose, and fructose rather than sucrose alone, the malformation was alleviated, and plantlets looked normal. Plantlets from hexose-containing media produced mature plants when transferred to soil. Plants expressing antisense mRNA for cell wall invertase had a bushy appearance due to the development of extra leaves, which accumulated elevated levels of sucrose and starch. Simultaneously, tap root development was markedly reduced, and the resulting smaller organs contained lower levels of carbohydrates. Compared with control plants, the dry weight leaf-to-root ratio of cell wall invertase antisense plants was shifted from 1:3 to 17:1. Plants expressing antisense mRNA for vacuolar invertase also had more leaves than did control plants, but tap roots developed normally, although they were smaller, and the leaf-to-root ratio was 1.5:1. Again, the carbohydrate content of leaves was elevated, and that of roots was reduced. Our data suggest that acid invertases play an important role in early plant development, most likely via control of sugar composition and metabolic fluxes. Later in plant development, both isoenzymes seem to have important functions in sucrose partitioning.

Invertases. Primary Structures, Functions, and Roles in Plant Development and Sucrose Partitioning

“…To study the functions of acid invertases in carrot, the antisense technique was used to generate transgenic carrot plants with reduced enzyme levels (Tang et al, 1999). Phenotypic alterations appeared at very early stages of development.…”

Crescimento de plântulas do milho 'Saracura' e atividade de alfa-amilase e invertases associados ao aumento da tolerância ao alagamento exercido pelo cálcio exógeno

“…Apesar de a função das invertases no período de germinação ainda ser pouco conhecida, sabe-se que elas clivam sacarose para fornecer hexoses como fonte de energia e carbono, regulando o turgor das células e promovendo a expansão celular, além de gerar um gradiente de concentração de sacarose entre órgãos fonte e dreno (TANG et al, 1999;MITSUHASHI et al, 2004;TAIZ e ZEIGER, 2004). Durante a fase de crescimento de órgãos ou células, a invertase ácida do vacúolo é a enzima com maior importância no suprimento desses açúcares (KOCH, 1996;TANG et al, 1999;MITSUHASHI et al, 2004).…”

“…Durante a fase de crescimento de órgãos ou células, a invertase ácida do vacúolo é a enzima com maior importância no suprimento desses açúcares (KOCH, 1996;TANG et al, 1999;MITSUHASHI et al, 2004). Os resultados observados com o milho 'Saracura' por FRIES (2003) corroboram com esses autores quando, tanto na parte aérea quanto em raiz, a invertase ácida do vacúolo teve as mais altas atividades.…”

“…Essas enzimas têm papel importante no metabolismo celular, no desenvolvimento do tecido e no crescimento do órgão, por fornecer hexoses que serão utilizadas como fonte de carbono ou como moléculas sinalizadoras. As hexoses produzidas pelas invertases também podem aumentar o potencial osmótico celular (KOCH, 1996;TANG et al, 1999;MITSUHASHI et al, 2004). Todavia, a função dessas enzimas no período de germinação e sua participação no desenvolvimento inicial de plântulas ainda é pouco conhecida.…”

Gene expression patterns of invertase gene families and modulation of the inhibitor gene in tomato sucrose metabolism

“…This finding is consistent with published data (Godt and Roitsch, 1997) and suggests that Lin6 plays a major role in vegetative growth. Moreover, the Lin6 gene was induced by glucose, zeatin, brassinosteroid, elicitors, and wounding (Godt and Roitsch, 1997; Tang et al, 1999). Lin6 expression may be regulated by endogenous hormones during vegetative growth.…”