ROOT SIGNALS AND THE REGULATION OF GROWTH AND DEVELOPMENT OF PLANTS IN DRYING SOIL

I NTROD UCTI ON. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 55 CHEMICA L A ND H YDRAULI C SIG NA LI NG . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 56 Soil Drying and Leaf Water Status........ ....... . . . . . . .. . . . . 56 Regulation of Plant Development: a Role for the Root? 57 Why Is a Root Signal Needed 10 Regulate Development? .. . . . . . . . . . . . . . . 59 How Can Plants 'Measure' Water Availability? 60 NAT URE OF THE CHEMICA L INFORMA T ON CONVE YE D FROM R OOT S T O SH OOTS .. . . . . . . . . . . . .... . . . . .. . . . . . . . . . . . . . 62 Positive 63 Negative and Accumulative Signals ....... . ......... . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . ... 67 Other and Some Problems ...... . . . . . . .... 68 CONCLUSIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..... . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70