Mudas de Coffea canephora, clone 109A, foram cultivadas em casa de vegetação e submetidas a duas taxas de imposição do déficit hídrico, utilizando-se, para isso, de vasos de diferentes volumes: 6 L , taxa rápida; e 24 L, taxa lenta. As amostragens foram feitas quando as plantas atingiram um potencial hídrico de antemanhã (Yam) de aproximadamente -2,0 MPa (déficit moderado ) e -4,0 MPa (déficit severo), sendo necessário, para isso, 4 e 6 dias nas plantas dos vasos de 6 L, e 12 e 17 dias naquelas dos vasos de 24 L, respectivamente, após suspender-se a irrigação. Avaliaram-se, então, em dois horários do dia, as concentrações foliares de hexoses, sacarose, amido e aminoácidos livres totais, além das atividades de enzimas-chave no metabolismo do carbono metabolism (AGPase, invertase ácida, SuSy, SPS, FBPase) em folhas de café, em resposta às taxas de imposição e níveis do déficit. Os resultados sugerem que plantas submetidas à seca apresentaram respostas diferenciadas no metabolismo de carboidratos, em função do tamanho do vaso de cultivo utilizado e, portanto, da taxa de imposição do déficit hídrico: enquanto nas plantas dos vasos pequenos houve redução na exportação de fotoassimilados e acúmulo de hexoses, provavelmente a partir da degradação de sacarose e amido, nas plantas dos vasos grandes verificou-se manutenção da exportação de fotoassimilados e, por conseguinte, do crescimento (provavelmente de raízes), ainda que a taxas reduzidas. Essas respostas, mais evidentes sob déficit severo, revestem-se de grande importância no processo de retardamento da desidratação. Contudo, as atividades de enzimas-chave do metabolismo do carbono foram pouco afetadas pelas taxas de imposição do déficit.
Seedlings of Coffea canephora, clone 109A, grown under greenhouse conditions, were grown in pots containing either 6- or 24-L of substrate, which allowed, respectively, two rates of progression of water deficit after withholding irrigation. All samplings and measurements were performed when predawn leaf water potential approximately -2.0 (moderate water deficit) and -3.0 MPa (severe water deficit) was reached. This was achieved at 4 and 6 days, or at 12 and 17 days after suspending irrigation, respectively, in plants grown in small and large pots. Concentrations of hexoses, sucrose, starch and total free aminoacids, and activities of key enzymes of carbon metabolism (AGPase, acid invertase, SuSy, SPS, FBPase) in coffee leaves, as affected by rates of progression and severity of water deficit were evaluated at early morning and early moon. The results suggest that changes in carbohydrate metabolism depended on pot size, and thus on the rate of progression of water deficit: in plants grown in small pots, assimilate export was reduced paralleling an accumulation of hexoses, due likely to sucrose and starch breakdown, while in plants grown in large pots, assimilate export was maintained, which should have allowed an extra root growth, even though under low rates. These responses, observed mainly under severe water deficit, are of major importance for dehydration postponement. However, the activities of key enzymes of carbon metabolism were only slight affected by rate of progression, as well as severity of water deficit.
